In general, the problem of evil has historically been a recurring blemish against the claim that Christianity is an internally coherent, and reasonable, belief system. In this project I will give a presentation of Thomas Aquinas' metaphysical solution to the metaphysical problem of evil. It is my intentions in this work to help further a more adequate understanding of not only Thomas Aquinas, but also give an exposition of the type of detailed analysis that he presents in his writings. However, this paper should not be seen as a complete apologetic work, but only as a demonstration of the internal coherency between the Christian notion of God and the metaphysical problem of evil. Nonetheless, if this project could contribute to that end, then I have, in part at least, accomplished my goals.
I would like to thank Fr. Michael Dodds, O.P., Fr. Stephen Ernest, S.V.D., and Fr. Edward Krasevac, O.P., from the Dominican School of Philosophy and Theology; and Rev. Donald L. Gelpi, S.J., from the Jesuit School of Theology at Berkeley; and finally Dr. John J. Glanville from San Francisco State University, for their proof reading of this work. However, I take full responsibility for any errors found either in substance or otherwise. Finally, I am indebted to my wife Jeanette's continual stability, love, and patience in my never-ending pursuit of "fides quaerens intellectum."
In the field of Philosophy of Religion there is a fundamental area of research for both the philosopher and theologian, and this is usually expressed as "the problem of evil." Depending on what angle the issue is looked at, there can be numerous variations or approaches to solving the problem of evil.  Of course the problem of evil does not emanate in a vacuum. The problem that I will be referring to is usually discovered arising within a particular notion of theism.  The formulation of the general problem of evil is that if there is an all-knowing, all-good, and all-powerful God who created this world, how is it that there is evil? The dimension of evil though that we are concerned with is the metaphysical problem of evil that comes primarily via the antitheistic argument that: 1) God is the creator of everything, and 2) evil is a thing, therefore, 3) God created evil.  This argument compels the theistic thinker to address several sticky issues; not only does the theist have to give an account on what is evil, but he or she must address what the cause of evil is, and whether or not God is ultimately that cause.
In this paper I will focus on the metaphysical formulation of the problem of evil, and its classical metaphysical response via Thomas Aquinas. Because this paper focuses on Aquinas’ response to the metaphysical problem of evil, I must spend some time laying out in greater detail his metaphysical outlook. In doing this we will be better able to understand his position of evil as a privation; for without understanding the notions of ‘matter’, ‘privation’, and ‘form’, to a certain degree, we will not be able to understand the place evil has in his metaphysics. Similarly, without a brief, but reasonable, account of his causal principles we can not even begin to address the question of where evil belongs in the causal structure. The causal principles are crucial to Aquinas’ answer that evil is a privation, and that God can not be the cause of evil. As a result, we will briefly address the four causes regularly utilized within the Thomistic/Aristotelian worldview. We will then apply the theory of evil as a privation within the causal explanations; this will help us understand the answer as to how things can be evil. And this will naturally lead us into the question of whether or not God can be the cause of evil, which will be the final issue discussed.
Usually, the typical kinds of responses to the problem of evil are claimed to be either a defense or a theodicy. The brief account of a theodicy is that there is a justification of the actions of God for allowing evil; a defense claims to show that the antitheistic arguments against theism, via the problem of evil, are ineffective.
The burden on the theist then would be either to defend, by way of an adequate argument, the coherence of theism; and/or justify, by way of an explanation, the existence of evil in a Judeo-Christian worldview. Even though there is a distinction made between a defense and a theodicy, there seems to be no a priori basis for rejecting the claim that the explanation, as understood as a defense, may also be utilized as a theodicy. 
My contention is that we only need to argue for the possibility (i.e., noncontradictoriness) of God creating a world in which real evil can, and does exist; and that God can not be the cause of such evil. If this can be done, then the necessary and sufficient condition has been met for establishing an internally coherent system; at least when considering the relation between the cause or causes of evil and the Christian notion of God. If these factors can be shown, then the burden has been lifted; hence, internal coherency has been adequately established for God and the existence of real evil; all the while, eliminating God as the cause of this evil.  However, this form of argument by no means proves, or is meant to prove, that Christian theism is true; its goal is to demonstrate internal consistency between the cause and real existence of evil, with the notion of the Christian God. For even though Christianity would be internally consistent, when advancing the relation between evil and God, this does not show the inconsistency of other worldviews, nor does it rule out the possibility of other contrary views to Christianity being internally consistent. 
I also would like to suggest that the metaphysical explanation should be considered as a preliminary and foundational stage in explaining the consistency of the relation between evil and the Christian God. For the metaphysical explanation must be antecedent to the moral or physical explanations.  The moral and physical problem of evil may generally be accounted for in the metaphysical one, but that does not mean that the metaphysical answer is a thoroughgoing answer for the general problem of evil within Christian theism. It does mean that some of the moral and physical evils may be explained under the metaphysical solution.
As stated above, the metaphysical problem is specifically ‘what is evil’  ; and secondarily, regardless whether it is a thing or not, ‘what is the cause of evil?’  The moral problem of evil attempts to resolve the question of ‘why’ is there evil; thus, the theist usually appeals to the notion of human free will to give an account for the ‘why’ question. The physical problem of evil addresses alleged unnecessary evils that are believed to not arise from human freedom (such as earthquakes). Thus, the theist may appeal to some form of providential necessity for evil, which in some cases, can be reduced to the answer given for the moral and/or metaphysical problems of evil. Likewise, appealing to human free will is at times not only a solution for moral and physical evils, but also some metaphysical evils as well. 
In this paper though, we will focus on the metaphysical solution to the metaphysical problem of evil as stated on page one; namely, the problem
is commonly understood as: God created everything, but if evil exists, then doesn’t that mean God created evil? We should clearly see that the classical position could not hold to any conclusion that suggests God created evil. It is true that God created everything, but does the theist need to accept the second premise, which suggests that evil is a thing? But if evil is not a thing, then is it an illusion? Again, the Christian can not accept the illusionary response as an account for evil; for evil has not been traditionally explained in this manner, nor is this explanation consistent with what Scripture says about evil. Neither can the Christian accept some form of dualistic worldview that suggests an evil deity versus a good deity (e.g., Zoroastrianism or Manichaeism); for then we have God not being perfectly sovereign. Surely scripture, tradition, and common sense, have taught us that evil is real; and surely Scripture and tradition teach us that there is only one true God—Yahweh—who has perfect sovereignty. But in what sense then is evil real? And what coherent account can be given to explain what evil is; furthermore, what can be said about the cause of such evil?
Thomas Aquinas was a Dominican Friar of the 13th century. The roots of his classical response can be traced back to St. Augustine. So let us now see what Aquinas had to say about the metaphysical problem of evil.
Aquinas addresses the same problem that was presented on page one. He states his opponent’s position as such: "Everything created is something. But evil is something created, as is said in Isaias [sic] (5,6-7), ‘ . . . I am the Lord making peace and creating evil . . ..’ Therefore evil is something."  Using the same terms as Aquinas, 1) If God created everything, and 2) evil is a thing, then 3) God created evil. His interlocutor’s position is further supported by several arguments that are meant to suggest that evil has a cause as a substance and is not a mere privation of the good. Since they are opposites (good and evil), and there are degrees of each between the two extremes, then they must be first principles. But if evil is a first principle for all that is evil, then evil can not be a privation of good.  To further argue that evil is a substance his interlocutor suggests that: " . . . everything that corrupts, acts. But evil, precisely as evil, corrupts, as Dionysius says. Therefore evil, precisely as evil, acts. But nothing acts except inasmuch as it is something. Therefore evil, precisely as evil, is something."  His opponent’s position attempts to argue that evil can not be a mere privation of good. Aquinas presents his opponent’s view that is allegedly supported by appeals to reason, scripture, and tradition; however, Aquinas does not buy into it, and furnishes us with a response. Aquinas argues that it is true that God created everything, but evil is not a thing. Now of course Aquinas is not suggesting that evil is not real, rather he is arguing that it is not a substance. That is, it does not exist in-itself, but only as inhering in a good substance. Without a good substance there could be no evil. This is the traditional Augustinian move that evil is a privation. That is, a ‘lacking’ of the good. In Aquinas’ Compendium of Theology he lucidly states this doctrine of privation:
. . . As the term good signifies ‘perfect being’, so the term evil signifies nothing else than ‘privation of perfect being’. In its proper acceptance, privation is predicated of that which is fitted by its nature to be possessed, and to be possessed at a certain time and in a certain manner. Evidently, therefore, a thing is called evil if it lacks a perfection it ought to have. Thus if a man lacks the sense of sight, this is an evil for him. But the same lack is not an evil for a stone, for the stone is not equipped by nature to have the faculty of sight. 
This concept of evil as privation needs some unpacking, for it is a metaphysically complex notion.  His example of the stone lacking sight versus the human being lacking sight is of some help. But the question is, in what sense is Aquinas saying the stone lacks sight versus the human lacks sight? Are they used in the same sense? If they were used in the same sense, then it would be ‘lacking’ in the same way. Surely then, Aquinas is not using ‘lacking’ in the same way.
In order for us to answer these questions we must turn to chapter two of Aquinas’ De Principiis naturae,  it is here that he addresses this distinction of ‘lacking’ as understood in two different senses. He starts out by presenting three principles of natural change; viz., matter, form, and privation. He says, concerning matter and privation, that "matter and privation refer to the same subject, but according to different reasoning."  What does this mean? A simple way to understand what he is trying to say here is that when we refer to, for example, the ‘morning star’ and the ‘evening star’, or ‘John Wayne’ and ‘Marion Morrison,’ the referent is the same for each subject, but the sense in which it is used is different.  Similarly, matter and privation are referring to the same subject, but in a different sense. A lump of bronze is both matter and privation, i.e., bronze is deprived of shape, but only a privation accidentally. The bronze lump has the potential to be a bust of Aristotle when melted and appropriately shaped according to his likeness; and as such, it is only accidentally deprived of the shape of a bust of say, Plato (hence only accidental form).
Aquinas continues his division, and separates accidents into two kinds: necessary accidents versus non-necessary accidents. An example of a necessary accident would be ‘a triangle’s angles equal the same as two right angles’; and an example of a non-necessary accident would be something like ‘discovering a pirate’s treasure while digging a hole for a plant’ . We can see that it is the nature of the thing (substance) itself that dictates the necessity, or non-necessity, of an accident. The fact that I am wearing a blue shirt is a non-essential (non-necessary) accident for me. However, the fact that I seek the good, or knowledge, is an essential (necessary) accident for me. 
The result of this brief description is that for Aquinas privation is clearly an accidental principle, but necessary for change. That is because matter never is completely absent of privation. The way to understand this better would be to imagine a bust of Plato having the form of the likeness of the actual Plato. But it is also, as a bust of Plato, deprived of the likeness of Aristotle, i.e., Aristotle’s face and head. In other words, it has the potential to be melted down and receive the form of Aristotle’s face and head. Aquinas says, concerning matter, "inasmuch as it [matter] is under one form, it is deprived of another, and vice versa." 
Now form itself is that "toward which generation moves."  In other words, the actual artist actualizes what is only potential in the bronze, but actual in the artist’s mind (namely, the form of the bust of Plato or Aristotle, et al.). And the form of Plato’s bust is the end or telos, but that end or telos is not possible without the antecedent principles of matter and privation, along with the antecedent conditions of that form actually being already in nature, or the mind.  Without matter, and without the lacking of form, or without the condition of potentiality (privation) there could be no bust of Plato or Aristotle (accidental forms). But we should keep in mind that the form of the bust of Plato is only an accidental form, i.e., it is only being accidentally and not substantially. It is possible that the bust could have been of Aristotle, et al. Some of these form-matter complexes are, or were, substantial in nature (e.g., both Plato and Aristotle actually existed in nature as substantial beings), but are not substantial in art; in art they are only accidental. The forms of the busts of Plato and Aristotle are not accidental forms alone, for they both, in these examples, were substantial form-matter compositions in nature. Plato, the human being, as a substance in potentiality, may acquire numerous accidental forms, such as the accidental mode of being a musician, an athlete, etc.; but these are only accidental changes/forms, and are not necessary for Plato to be who he was. If Plato should undergo a substantial change to his being, which in fact he did, he would cease to be. Aquinas articulates this in the following quotes:
There are certain things which can be [esse] but do not, and others which are.  Those which can be [and are not] are said to be in potency, whereas those which already are, are said to be in act.
He goes on to elucidate on the distinction between substantial being versus accidental being:
. . . [T]he matter that is in potency to exist substantially is called matter out of which, whereas the matter that is in potency to be accidentally is called matter in which. Likewise, properly speaking, what is in potency to be a substance is called prime matter, whereas what is in potency to be accidentally is called a subject. Accordingly, accidents are said to be in a subject, but substantial form is not spoken of in this way . . . form makes matter be, whereas an accident does not make a subject be. The subject, however, makes an accident be . . . . What makes something to be substantially is called substantial form, and what makes something to be accidentally is called accidental form. 
At this juncture let us now summarize: 1) The three principles of natural change are form, matter and privation. We saw that Aquinas believes that prime matter and privation are metaphysical principles that work together.  And we further saw that form and prime matter are the metaphysically necessary principles for different modes of being. Without prime matter and form you have no natural being, and without privation, you have no natural being, the three are necessary for natural change. The result is that all matter is in potency and that matter must have form to be. 2) We also found that natural being is in both potency and act. There are modes of being that are in potency accidentally (e.g., the form of the bust of Plato, or the accidental qualities of being a musician, a chess player, etc.). And there are modes of being that were or are in actuality substantially (Plato, as a finite human being that actually existed, thereby, also in potency, as in the process of acquiring different modes of being accidentally). Accordingly, all accidents are said to be in, or dependent on, a subject; so, for example, the mode of being of the accidental form of ‘white’ is an accidental form that depends on its being in Plato’s substance (i.e., substantial complex of matter/form). 3) We also discovered that accidental being could be either necessary or non-necessary. In other words, its (i.e., the accidental form’s) mode of being is necessary when it can not be, at least conceptually or metaphysically, separated from the substantial being in which it is dependent on. So, for example, a triangle has the accidental mode of being of ‘angles equaling two right angles’ which is a necessary accidental mode of being. And the ‘discovering a lost treasure while digging a hole for a plant’ is a non-necessary accidental mode of being. Likewise, the actual playing of classical piano is a non-necessary accidental mode of being. Or the fact that Plato was a philosopher is a non-necessary accidental mode of being dependent on Plato’s substantial mode of being.
Two final crucial inferential points can be made from what has been given so far: namely, 1) that the nature of the substantial being will dictate the restrictions of the mode of being for the accidental form. In other words, whether the accidental mode of being is necessary or not, depends on the nature of the substantial being it is dependent on. 2) Whether or not the substantial being has a real privation also depends on the nature of the substantial being. For the stone can not have a real privation of sight if it is a stone, but a human can. For human nature dictates at least the potentiality for sight. Whether that sight is actualized or not is another question. Similarly, the fact that my substantial being has the accidental mode of being of playing classical piano and my wife does not, (i.e., all things being equal, she only has the accidental mode of being of potentially playing classical piano), makes her have a real privation of playing classical piano. She has the potential to do so, but it is not actualized as it is for me, and clearly playing piano is a nonessential accidental mode of being. However, Buford the dog is not in privation of the accidental mode of being of playing classical piano, for it is not even a potentiality within a dog’s nature to play classical piano.
So now we need to address the issue of what Aquinas means by "lack" in the context of what has been stated so far. Thus, at this juncture, we are primarily concerned with in what sense does the stone "lack" sight, and in what sense does the blind man "lack" sight? Aquinas says:
Although generation is from not-being, one should realize that we maintain, not that negation is a principle, but rather that privation is, for negation does not determine a subject for itself. Not to see can be attributed even to non-being, for example, "Chimeras do not see." Likewise, we can attribute it to beings that are not meant to see, such as a stone. But privation is attributed only to a determinate subject in which the missing perfection is meant to be. For example, blindness is attributed only to those things that were born to see. Moreover, it is in accordance with the fact that generation does not arise from non-being simply, but from nonbeing which is in some subject—and not just any subject, but a determined one—that privation is said to be a principle. For not everything which is not-burning will burn, but only those things that are apt to burn . . . privation is an accidental principle, as has previously been explained; the other two [form and matter] are essential principles. 
Here we should have a clearer picture of what Aquinas is trying to suggest; viz., when we talk about something having an absolute negation of an accident (whether essential or not) we are talking about the absolute incapacity of that being for even having that accident (one sense of ‘lack’). So, a rock does not have within its nature the capacity for sight, but a human does. A human has the potentiality for sight (e.g., a zygote); and similarly, as humans we can be in privation of sight (e.g., blindness) for it is the ‘lacking’ of a perfection that we should have; but a rock lacks this potentiality absolutely.  A rock is in absolute negation of both the capacities to actually see and the potential to privation of sight; because within its nature there is the absolute negation of this capacity for privation of sight and even the potential to actualize sight.
The Four Causes
Now before we answer the question of how modes of being, and the principles of natural change are related with the privation of evil, let us first address Aquinas’ position on the causes. Doing this will further help us understand his answer to the metaphysical problem of evil. For if evil is simply a privation of good, and not a substance in and of itself, then ‘what causes evil’? (if it even has a cause) would be the next logical question to address. 
In Aquinas’ De Principiis naturae, he addresses these causal principles. For Aquinas, everything that is in the mode of being of act/potency must intend to act to an end. Of course Aquinas does not imply that all things that act do so intentionally via deliberating, for this would be absurd. Those things that can deliberate on what ends to strive for can act to choose one end over another, but everything else is determined to an end. But there are acts, such as involuntary acts, that are still intentional, but not deliberated by agents that have the potential to deliberate an act.  For example, blinking is an intentionally
determined act. That is, the agent (human being) intends an end by blinking (which may be for the health of the eyes); and clearly, this intended end is not of deliberation for the agent (at least the involuntary blinks). Similarly, when I play a certain chord on the piano, there is no deliberation between the notes, i.e., there is no need for me to play the notes individually to figure out which notes comprise the chord--they are predetermined.  My purpose is to play and hear America the Beautiful and the means for completing this end is also intended, but not deliberated. The point Aquinas is trying to emphasize is that acts have a "natural inclination toward something."  The act of playing certain chords comes naturally for the pianist; one does not have to deliberate over which notes make up the specific chord. So for Aquinas, all things ‘intend’ to an end via deliberation or natural inclination.
Aquinas then continues in chapter two and lists the four causes: material, efficient, formal, and final, two of which are considered to be intrinsic (matter and form), and two of which are considered to be extrinsic (efficient and final). Additionally, Aquinas points out that we should not confuse a cause with a principle, in some cases we will find a relevant difference. There are examples where a principle is not a cause; for example, the principle of privation, since it is only an accidental principle, it can not be an essential cause.  Privation is a principle of change, but not a cause of change, hence, it could not be considered as an essential cause. We can understand this better by noticing that, for example, the color black is the principle of white changing, but not the cause of white changing. Aquinas gives us a strict definition of what a cause is:
. . . [A] cause is said to be that out of whose being another being follows. Accordingly, what is prior by way of being that by which motion starts cannot be called an essential cause, even if it is called a principle. This is the reason for including privation among principles, but not among causes. A privation is that from which generation departs. It can, however, be called an accidental cause, inasmuch as it coincides with matter . . . [emphasis added]. 
His point should be apparent, since privation is not a mode of being, for there is no being out of which privation brings about another being, privation can not be considered as a cause, but only as a principle of change. Privation is a necessary condition in order for change to occur, but change will not occur due to privation alone.  Change is caused by efficient, material, formal, and final causes, and privation is not an essential cause, but a principle of change. Let us, by way of example, explain what role each of these causes would then play in relation to different modes of being.
An actualized sperm and ovum are potentially a human being (i.e., an actual being as sperm and ovum, but also a being in potency to be human), which upon their uniting (the natural inclination of both the sperm and ovum) become an actualized zygote (actual human), but also a unique individual person; i.e., the zygote has the potential (natural inclination) to choose, act, love, dream, reason, grow, etc. (all activities that may or may not come to fruition in a person). Of course, whether a particular zygote does actually manifest these accidental modes is a different question altogether.  Nonetheless, the potentiality is present, unlike for a stone. The privation of the act of reasoning is a real lack for the zygote, but not for the stone. We can also see, by this example, that the secondary efficient cause by which the zygote comes to be, is both the mode of being of the sperm and ovum (extrinsic causes), and the mode of being of both parents (extrinsic causes).  The primary efficient and existential (or sustaining) cause of the zygote would of course be God as both the initiating (or efficient) cause and sustaining cause of its being. Additionally though, we can consider the mother as not only a secondary efficient cause, but also as a secondary existential cause; this is so because she is the human incubator whose actual substantial being sustains the being of the zygote.  The sperm and ovum have passed from a mode of being that is both actual and potential, to a zygote that is in both act-potency. Even though the zygote will mature in its natural course of development—through sustenance, education, relationships, etc. (accidental instrumental causes)—these are only accidental changes, not changes in its substance. The formal cause is, of course, the substantial form of the human being, namely, the human soul, that by which a human is human. The material cause is that out of which we are made—the prime matter which has the possibility of existing as human. The secondary exemplar cause would be that after which the zygote comes to be—the parents, while the primary exemplar cause would of course be God, because we are all made in the image of God. And lastly, but by no means the least, we have the final cause, that for which the zygote came to be. This answers the crucial question of why something happened. Hence, the question for why the zygote came to be (i.e., what is the final cause of the zygote) is for communion with God. In this example  we can clearly see how the causes can work together. Further, it is God’s act as the primary efficient and sustaining cause that brings it full circle to him as the final cause also. There is some real metaphysical truth in the fact that God is both the Alpha and the Omega.
At this point we should have a clearer understanding of both the meaning of privation and its different senses; furthermore, we should see (by my example) the interdependent role, and different significance, that each cause plays in relation to the modes of being. This is all the more apparent when considering the role that accidental causes versus essential causes play in the solution for the cause of evil. We are now ready to examine these metaphysical notions in relation to the metaphysical problem of evil.
But before doing this there is one more point that needs to be more explicitly laid out in order for us to complete Thomas’ metaphysical picture. For Aquinas, as I alluded to above, all things strive (naturally or otherwise) to an end, but additionally, all things are determined to a good.
That every agent acts for an end has been made clear . . . [but] . . . the agent would not be inclined to it except by virtue of some agreement with it. But, what is appropriate to something is good for it. So, every agent acts for a good. 
The point that Aquinas is stressing, and which he argues for, prior and subsequently to this text, is that all things have a natural impulse or intellectual faculty to act to an end; but that end must be good for it. For the end is determined by some natural desire. And nothing is naturally inclined to act in such a way that is contrary to its own good, for the good "provides the terminus for appetite . . . [t]herefore, every agent acts for the sake of a good."  Another way to look at this is to say that since all things act for an end and all things desire (naturally or otherwise) the good, and being is good, then all things desire being/good. 
How about that evil?
What can we now say about Aquinas’ assessment of evil? First, evil is not a thing, that is, it is not a substance; hence, it has no essence. He states:
. . . [E]vil is simply a privation of something which a subject is entitled by its origin to possess and which it ought to have, . . . privation is not an essence; it is, rather, a negation in a substance. Therefore, evil is not an essence in things. 
Second, since evil is not a substance, but a privation of a good substance, evil can not ‘wholly’ corrupt some thing.  The reason is that there is no-thing there for evil to subsist in. Aquinas says that: " . . . no matter how much evil be multiplied, it can never destroy the good wholly."  Additionally, the explanation that evil is not a substance, brings in the third crucial point that needs to be addressed; viz., if evil is not a substance (not a form-matter composition), then what could be the cause of evil? This latter issue also implicitly brings up the question of whether or not God is the cause of evil.
Clearly, given the construction of the causes given above, and the notion that evil is not a substance, what follows from this is that evil does not have a formal cause per se; for only that which is substance can have form, evil is not a substance, hence evil has no form. Evil, by definition, is the privation of form.  What then can we say about the final cause of evil? With this too, evil can not have a final cause, for only substances that move toward fruition of perfection or increase of order can have a final cause.  Evil is neither a substance, nor that which desires/intends naturally to order/perfection, hence, evil does not have a formal or final cause per se. Aquinas articulates as much in the following quote:
. . . [T]hat which has a per se cause is intended by its cause, for what happens outside the agent’s intention is not a per se effect but an accidental effect, for example the digging of a grave is accidentally the cause of finding a treasure when this happens outside the intention of the gravedigger. But evil as such cannot be intended, nor in any way willed or desired because the desirable has the nature of good, to which evil as such is opposed . . . every per se cause has a fixed and determined order to its effect, and what is done in keeping with order is not evil, but evil occurs when order is neglected; hence evil as such does not have a per se cause. 
Now we should consider the material cause of evil. If evil is not a substance, and all that is, is good, then (following the act/potency principle) the only material cause for evil is a good substance. So, the material cause for evil must be, at least accidentally, a good substance.  That implies there is no essential evil material cause.  Aquinas again expresses as much in the following quote:
Now everything which is accidental, is reduced, i.e., is traced back to that which is per se; but if evil does not have a per se cause, as has been shown, it remains that only good has a per se cause. Nor can the per se cause of good be other than good, since a per se cause produces its like. It remains then that good is the accidental cause of any evil. But evil, which is a defective good, may also be a cause of evil; nevertheless it always comes back to this that the first cause of evil is not evil, but good . . . evil is accidentally caused by the good, either by virtue of the matter of the effect, or by virtue of its form. For, if the matter is not well disposed to the reception of the agent’s action on it, there must result a defect in the product. 
Is God at fault?
What now can be said about an efficient cause for evil? This question is indeed related to the metaphysical problem of evil; viz., if only good substances could be the per accidens cause of evil, what then causes evil as a per se efficient cause, would it not be God then? Are not per accidens causes reduced to per se causes? How can one avoid God as the metaphysical efficient cause of evil, if indeed God is the efficient cause of all good substance, it seems then that God would be the efficient cause of evil? Let us turn to Aquinas and see how he addresses this problem. The argument that God would be the cause of evil proceeds as follows:
. . . [T]he effect of the secondary cause is reduced to the first cause. But good is the cause of evil, as was said above (A.1). Therefore, since God is the cause of every good, as was shown above (Q.2, A.3; Q.6, AA.1, 4), it follows that also every evil is from God. 
In general Aquinas responds to this problem by first making a distinction between evil as fault and evil as penalty. For Aquinas, evil considered as penalty is caused by God as the efficient cause, but only as per accidens. In particular, Aquinas argues that it is within the nature of an ordered teleological cosmos to be a just cosmos. And punishment would be necessary
in order to maintain an ordered and perfecting end in consideration of such a cosmos that is comprised of imperfect beings. He elaborates on this in more detail in the Christian notion of divine providence. 
When discussing evil as fault though, Aquinas turns away from looking at God as the per accidens efficient cause of this evil, for the efficient cause of fault lies in an imperfect being’s will or the pre-existing material deficiency. But since God is perfect, in the sense that he lacks nothing, and is wholly actualized , he can not be the efficient cause of imperfection. Only an imperfect being (that which lacks) can be the efficient cause of imperfection, but again only accidentally; hence, the efficient cause of the imperfection of the evil of fault would lie in the imperfect agent’s will or pre-existing material imperfection. Aquinas wants us to further notice that the intentions of God are not to bring about such evils, but such evil as penalty is necessary for a teleologically greater good:
But it is manifest that the form which God chiefly intends in things created is the good of the order of the universe . . . and thus God, by causing in things the good of the order of the universe, consequently and as it were by accident, causes the corruption of things . . . [emphasis added]. 
Let me elaborate further by the following analogy: Let us suppose that a bicycle manufacturer specialized in making tricycles. One day the parents of Rachele bought her one of those fantastic tricycles. Now Rachele was an autonomous, free-willed little girl who seldom took her parents advice.  One day Rachele was pushing her tricycle to its limits, indeed she was going so fast that she lost control and fell. Unfortunately, she bumped her head and ultimately required some stitches to close the wound (the unfortunate consequences, or penalty, for not accepting the wisdom of her parents). However, her parents felt it was the fault of the manufacturer for making a defective tricycle, and they wanted to sue them (penalty). But, upon investigation it was discovered that Rachele was careless in her behavior, and the manufacturer was found to be free of any culpability. From that point on Rachele began being more cautious with her freedom and taking better care of her tricycle.
The manufacturer of the tricycle was not found to be culpable for the accident, nor could the manufacturer be found to be the per se cause of the accident, in fact we can only see the manufacturer as a per accidens cause in the sense of creating the tricycle in which to help Rachele enjoy her play time. Additionally, we can see that due to Rachele’s lacking of knowledge (privation) of the proper way to behave while on the tricycle, we see her (and possibly her parents too) as a secondary per accidens cause for the evil consequences.
As a result, we can see that the question of the efficient cause per accidens of evil lies squarely, and primarily, in the dimension of the imperfect beings in evil as fault and only accidental providentially by God when evil is considered as penalty.  However, God is only the accidental efficient cause for the necessary  evils within the scope of his divine providential control. Ultimately, it appears that all evils are necessary, at least those evils in the sense of bringing about perfection and justice in an imperfect cosmos in relation to penalty.  And when considering the efficient cause he does make a distinction between those evils that require fault and those evils that require penalty. The former rests in the agent causation of the imperfect will and pre-existing material deficiencies, but only via per accidens; while the latter evils’ causes rests via per accidens within the providential intentions of God for the imperfect beings to be perfected.
Hence, Aquinas’ answer is:
The effect of the deficient secondary cause [imperfect being] as regards what it has of being and perfection, but not as regards what it has of defect; . . . And, likewise, whatever there is of being and action in a bad action, is reduced to God as the cause; whereas whatever defect is in it is not caused by God, but by the deficient secondary cause. 
We can see that Aquinas has pointed out several important factors when considering the metaphysical problem of evil. In the beginning of this paper we laid out the antitheistic metaphysical problem of evil as follows:
- God is the creator of everything.
- Evil is a thing.
- Thus, God created evil. 
Obviously, if we accepted premises one and two the conclusion would not be the orthodox view of Christianity. Surely, God created everything, and surely evil is real; so, the problem then was in how one defined ‘thing’ in premise two. We found that, according to Thomas, evil is real but it is not a substance, instead it is a real lacking of what should be. So the argument above was then responded to in the following way:
- God is the creator of everything.
- Evil is not a thing, but a privation.
- Thus, God is not necessarily the creator of evil. 
However, after getting to this point Aquinas had to then explain what he meant by ‘substance’ or ‘thing’; and furthermore if evil was not a substance or thing, then what is it? He showed us that a substance is a primary matter/substantial form complex that is good; but evil could not fall under this category, for then God, as the creator of all that is good, would be the creator of evil. Also, by rejecting the notion that evil was a substance Aquinas avoided metaphysical dualism. Finally, by expressing evil as real, he avoids illusionism. Thus, we found that evil was not a substance, but a privation of some good that should be there. But we needed some clarity in what was meant by ‘privation’. For Aquinas, it was a sort of ‘lacking’ of the good that was not meant to be this way. But it was not an absolute negation as a rock not having even the potential to see; instead, it was defined much like a human being that is blind. Blindness is a real lack, and humans have the potential to see, and to lack this actuality is to be deprived of a mode of being that should be there. The result was that this evil was a real ‘lacking’.
Furthermore, we discovered that the cause of evil then could only be a good substance, for only that which is actual could bring about something real (ex nihilo nihil), and all that is actual is good. But in what sense is evil caused then? Since evil was not an actualized substance or essential principle it could not have, or be, an essential cause, nor could it have a formal or final cause. Instead, it was only a per accidens principle of change, and not the per se cause of change. Much like white is the principle of change to black in the sense that it must begin as other than black, but white is not the cause of the change to black. Thus, the cause of evil would then be a good substance only accidentally.
At that juncture we were then able to see that Aquinas had demonstrated not only that evil was a privation of being as a per accidens principle of change, but also that evil has no direct per se cause. He further showed us that good substance was the cause of evil only accidentally.
But the natural problem that arose then was ‘is not God then the cause of this evil, since all per accidens causes are reducible to the first principle?’ Thomas’ rejoinder was to make a distinction of evils of fault and evils of penalty. In the former, culpability rested squarely in the lacking in both being and will of the secondary per accidens causes of evil, namely, finite human being’s and their will, and the lacking of being found in other imperfect beings. The latter evil of penalty was necessary evil in order to contribute to the perfecting of the cosmos in that it was just for such penalty to occur. Without it the cosmos would not strive toward perfection, which is the natural intention of a perfect being such as God. As a result we found that it was not the intentions of God to have either kind of evil (privation), but nonetheless the evil of penalty is permitted in order for the cosmos to intend to a perfecting ordered and just cosmos. Hence, God is the efficient cause of evils only per accidens, i.e., only in the sense of God sustaining all being to progress toward an ordered and perfecting reality, hence God is not culpable. Second, we can conclude that all evils ultimately arose due to the secondary per accidens causes of finite and imperfect beings, as both fault and penalty. For if there were no imperfect beings there would be no need for penalty or fault.
No matter where one may stand concerning the relation of evil to the notion of a Christian God, it should be apparent, that to ignore Aquinas’ analysis of the metaphysical problem of evil would be leaving out an important thinker within the circles of both philosophy and theology. Regardless of today’s philosophical, and in some cases theological anti-Thomas thought, this author finds that not only is Thomas’ metaphysical explanation insightful, but it is indeed successful.
 (Feinberg 1979, 3.; Peterson 1998, 393-401.)
 Specifically, the traditional Judeo-Christian view.
 See the following for a general coverage of the issue of evil (Summa theologiae, Ia.48-49); see the follow for the antitheistic argument (De malo, Ia.1.1).
 It appears that Erickson makes no such distinction between a theodicy and defense. See (Erickson, 1998, 436-456).
 Of course this assumes that in some way the explanation of the cause or causes of evil will eliminate God as a possible culpable candidate; in particular, we will find that it is unavoidable, when discussing efficient causality, to bring in the question of moral culpability. At least to a certain degree the discussion of efficient causality will necessarily touch on the moral problem of evil. That will be addressed in chapter 3.
 My point here is that internal consistency alone would not be sufficient as an apologetic.
 Simply put, if one attempts to explain either moral or physical evil prior to metaphysical evil, then he or she would naturally have a preconceived notion of ‘what’ the nature of evil is and what is the cause of this evil. Hence, we must begin with explaining first what evil is and what is the cause of it, before one can explain why there is evil. Aquinas follows this same strategy in De malo, although he does not explicitly call this the "metaphysical problem of evil"; nevertheless, it is de facto what he is analyzing, i.e., the nature and cause or causes of evil (at least initially). You will also notice that the order of his presentation in the De malo follows a similar strategy appropriated in this paper: Article 1: "Whether Evil Is Something?", Article 2: "Whether Evil Exists in Good?"; (Articles 1 and 2 can be understood as concerned with the questions of what is evil from two senses; viz., both in-itself and in some ‘thing’. Article 3: "Whether Good Is the Cause of Evil?"; Article 4: "Whether Evil Is Properly Divided into Punishment and Fault?" Articles 3 and 4 deal with the cause or causes of evil. And naturally when dealing with efficient cause Aquinas wants us to distinguish not only per accidens and per se cause, but also understand how that will work out when it comes to the moral notion of culpability.
 The implication of premise two—"evil is a thing"—found on page one, compels us to address what ‘is’ evil, if not a thing?
 Taken from the conclusion of the argument found on page one: "God created evil." The implications for this conclusion, apologetically speaking, would be ‘what is the cause of evil,’ if not God? This must be responded to in order for one to adequately explain the causal framework for evil.
 For a good account of the theistic approaches for the metaphysical, physical, and moral scope of evil, from within a Protestant Thomist position, see: (Geisler and Corduan 1988, 295-385).
 (De Malo, Ia.1.1).
 Ibid., Ia.1.5,6,7.
 (Ibid,Ia.1.8.; Summa theologiae, 1a.48.1).
 (Compendium theologiae 114, 125-126).
 (Summa Contra Gentiles, III, 7).
 Throughout this paper I have used Dr. John Glanville’s corrections of the English translation to the Latin text of De Principiis naturae given in a graduate seminar on Aquinas at San Francisco State University.
 (De Principiis naturae, 2.8)
 For the reader that may not be familiar with these common examples given in philosophy of language, Marion Morrison was the name of John Wayne before he became an actor. With the star example, we have Venus seen in the West after sunset, and seen before sunrise in the East.
 Aquinas’ example of ‘risibility of man’ is hard for the contemporary mind to agree with, thus, I gave the example of the triangle. Also, I believe the latter example is Aristotle’s, although I can not recall exactly where it is in the text. Additionally, the fact that finding the pirates treasure is a ‘chance’ event is irrelevant to my point; for that does not negate it as a non-necessary mode of being.
 Aquinas held the Aristotlian teleological metaphysics. In particular though, with a somewhat slight difference to Aristotle’s notion of "All men by nature desire to know" -- Metaphysics Bk A .1, Aquinas said we seek the good and that good is God. Of course, Aquinas would likely suggest that when one seeks knowledge (assuming it is the True), he or she is implicitly seeking the good, and the good is ultimately God. See (Summa contra Gentiles, III, 1, 2&3.; Summa theologiae, Ia IIae, Q.1.; De Principiis naturae, 3.
 (De Principiis naturae, 2.9).
 (Ibid., 2.7 or 8 depending on the English translation of the Latin text used. (In Bobik it is 2.7, in Goodwin it is 2.8)
 This is a simple appeal to the principle of noncontradition--that something can not both be and not be at the same time and in the same sense. Hence, Plato’s form of his face and head, or the properties and/or conditions of it, must necessarily be, or have been (at least as an idea), at one time in order for Plato’s bust to come-to-be. One can not make something to be from nothing.
 Nota quod quoddam potest esse licet non sit, quoddam vero est. If this were literally translated it would be as follows: "Mark (take note) the fact that some thing may (can) be but do not be, there be other things which be." The relevance of my placing the literal translation is twofold: First, there is a common practice amongst some translators to put "exist" in place of "be," and second, in order to avoid such an uncritical translation I have incorporated the text here. As Dr. John Glanville, and other Maritain Thomists may point out, they do not like to translate ‘esse’ as ‘exists’ – it loses its raw meaning that someone reading the Latin would be able to get. It is better to use ‘be’ – it ties the concept of ‘being’ more firmly into the concept of ‘exists’ – which mere ‘exists’ in English lacks. I thank my wife Jeanette, and Dr. J. Glanville, for pointing this out to me.
 (De Principiis naturae, I).
 The reader should avoid blurring the distinction between the logical application of these principles (which make them metaphysical principles) with what they explain (viz., natural change). What should be understood is that these principles are metaphysical principles in the sense that they are applied to the physical in order to explain and understand natural change; but that would not make them solely physical principles (in one sense they can be considered as physical principles, but within another usage they are metaphysical ones too). A philosophy dictionary points this out most lucidly by defining metaphysics as: " . . . [T]he philosophical investigation of the nature, constitution, and structure of reality," see (Audi 1999, 563). Adler also lucidly describes Aristotle’s central books in the Metaphysics as: " . . . [T]reat[ing] of sensible, physical substances; their nature as substances; the distinction between substance and accident, form and matter, potentiality and actuality, as principles of the composite nature of changing substances; and the properties of such existences in virtue of their having being. . . .. " (Ader 1999, 538). So, the fact that I focus my discussion primarily from within Aquinas’s De Principiis naturae, is irrelevant when it comes to trying to have a clearer understanding of what Aquinas believes about these metaphysical principles, regardless where they are found. Aquinas also discusses these metaphysical principles in his Commentary on Aristotle’s Metaphysics Bk VIII, (by that above confused and odd logic it would make these principles only metaphysical ones, since that text is about metaphysics, but this would be absurd, for that is contradictory). Aquinas also discusses them in his Commentary on Aristotle’s Physics Bk I, Lec. 13; Bk II, Lec. 2. Thus, it seems completely incorrect to suggest that De Principiis naturae is "all physics, [and] not metaphysics," (as Fr. Dodds contends), for that not only confuses the fact of a distinction between application of metaphysical notions, from their potential for physical explanation; but additionally it would be inconsistent with both Aquinas’ and Aristotle’s view of these principles.
 (De Principiis naturae, II, 10 & 11).
 I actually see, but I also contain the potential for the ‘privation of sight’. That is I can go blind. Likewise, I as a zygote, had the potential to see, even though I did not actually see, or even able to exercise seeing at that point. But a big rock (analogous to the zygote) does not have even the potential to see (but has the potential to be smaller). As a result, applying not seeing (lack of sight) to a rock is not used in the same sense as applying privation of sight (lack of sight) to a human.
 Simply put, if evil is not a substance, then we need to not only account for its existence; but also, if we say it exists, then naturally we ask what causes it to exist.
 Intentional is not being used here in the same sense as found in the popular English colloquia, i.e., necessarily requiring an act of the will by the agent.
 My point here (which is taken from Aquinas’ briefer example of a cithara) is to exemplify that if one deliberates over what notes are to be played simultaneously, then one has now broken the notes into a succession (or a trill, or some variance thereof), and as such, would no longer be playing a chord. The act of playing a chord is predetermined, i.e., requiring no deliberation.
 (De Principiis naturae, 3.19).
 Thus, we will see that evil in-itself can not be an essential cause, but only an accidental cause and a principle of change.
 (De Principiis naturae, III.21.)
 We should also make note of the fact that this does imply the necessity of evil (discussed below).
 What accidental modes are essential or nonessential is rather irrelevant at this point. As a matter of fact, this is a rather controversial issue that neither space or time will allow me to address in this paper.
 The sperm and ovum and the parents are both instrumental causes too. Primary instrumental causes are the parents, but the sperm and ovum are considered secondary instrumental causes.
 The use of primary and secondary causes is common knowledge amongst Aristotelian thinkers, hence, my reason for not elaborating on this. But for those readers who may not be familiar with this terminology, the primary is considered as the first efficient cause, while the secondary is considered to be an aiding efficient cause for the primary efficient cause. Secondary causes are not necessary in every event, however, a primary cause is. My wife may tell me to take out the trash, then she would be considered the primary efficient cause of the trash being dumped (assuming I do take it out), then I am the secondary efficient cause. However, if I choose not to (which is suicidal) and she takes it out, she would be the primary cause, with no secondary cause. Additionally, I did not expound on the difference between existential versus nonexistential causes. Simply put, an existential cause is considered to be an ongoing sustaining cause; while a nonexistential cause is much like a one-time temporal cause. The father is a one-time shot as the donor of the sperm for the zygotes coming-to-being, he is clearly neither a direct or indirect primary or secondary existential cause.
 Taken from: (King 1998, 10-13).
 (Summa contra Gentiles, III, 1.3, 7,8,9).
 (De veritate III, 22.1 & 2; Summa contra Gentiles, III, 1.1.2, 3, 12).
 Put slightly different we have: " . . . if good is that which all desire, then being itself must be called a good, because all desire to be." See (Summa contra Gentiles, III, 7.3).
 Ibid., 3.7.2.
 (Summa theologiae, Ia 48 ad 4; Summa contra Gentiles, III, 12). We must keep in mind that Aquinas has two senses in which we can speak of evil; first, in-itself and second as the subject of evil. Here we are speaking of evil-in-itself. See: (De malo 1, Response).
 (Summa contra Gentiles, III, 12.1).
 " . . . But evil has no formal cause, rather is it [evil] a privation of form . . . ." See (Summa theologiae, Ia 49.2).
 " . . . [L]ikewise, neither has it [evil] a final cause, but rather is it a privation of order to the proper end . . .." Ibid.
 (De malo, Ia 1.3).
 Only what is in act can bring about substance, evil is not in act, hence, evil does not bring about substance. See (Summa contra Gentiles, III, 1.10 & 11).
 " . . . [E]very evil is caused by good, as was shown above (A.1), and because evil can be only an accidental cause, and thus it cannot be the first cause, for the accidental cause is subsequent to the direct cause." See (Summa theologiae, 1a 49.3).
 (De malo Ia 1.3; Summa theologiae, Ia 49.2). Thomas argues as follows: "Evil . . . has a cause by way of an agent, not directly, but accidentally . . . evil is caused in the action otherwise than in the effect. In the action evil is caused by reason of the defect of some principle of action, either of the principal or the instrumental agent . . . sometimes by the power of the agent, sometimes by reason of a defect, either of the agent or of the matter . . . [b]ut this very fact that it is a deficient being is accidental to good to which of itself it belongs to act. Hence it is true that evil in no way has any but an accidental cause; and thus is good the cause of evil . . . evil never follows in the effect, unless some other evil pre-exists in the agent or in the matter, . . . [b]ut involuntary things the defect of the action comes from the will actually deficient, inasmuch as it does not actually subject itself to its proper rule." It should be pointed out that these quotes, for the most part, address the efficient cause of evil. This will be covered more in Chapter 3.
 (Summa theologiae, Ia 49.2).
 (Ibid., Ia 22.3) " . . . [C]orruption and defects in natural things . . . are in keeping with the plan of universal nature; inasmuch as the defect in one thing yields to the good of another, or even the universal good . . ." (Ibid., Ia 22.2). Also, "Since God, then, provides universally for all being, it belongs to His providence to permit certain defects in particular effects, that the perfect good of the universe may not be hindered, for if all evil were prevented, much good would be absent from the universe." See (Summa contra Gentiles, III, 71).
 Aquinas defines perfect as " . . . which lacks nothing of the mode of its perfection." (Summa theologiae, Ia 4.1). And specifically for God, Aquinas says: "Now God is the first principle, not material, but in the order of efficient cause, which must be most perfect . . . [h]ence, the first active principle must needs be most actual, and therefore most perfect; for a thing is perfect in proportion to its state of actuality . . . ." (Ibid., Ia 4.1 Q.4; Summa contra Gentiles, III, I.28).
 (Summa theologiae, Ia 49.2).
 Clear case of ‘lacking’ wisdom of experience.
 We must keep in mind that for Aquinas evil as punishment is necessary for the maintaining a just universe, as such he says: " . . . [T]he order of justice has as an adjunct the privation of a particular good of a transgressor, inasmuch as the order of justice requires that a transgressor be deprived of a good he desires. So accordingly, the punishment itself is good simply, but an evil to this person . . . . it is clear that evil is said to be created not inasmuch as it is evil but inasmuch as it is good simply and evil only in a certain respect." [emphasis added] See: (De malo 1, Reply 1). "A wise provider does not consider what is good for merely one of the things that fall under his providence. He is concerned rather with what is better for all. Consequently, even though the corruption of a thing in the universe is not good for that thing, it is good for the perfection of the entire universe, because the continual generation and corruption of individuals makes it possible for the species to be perpetual; and it is in this that the perfection of the universe essentially consists." (De veritate, 5.3 "Answers to Difficulties" 2).
 Throughout Aquinas’ use of evil as being necessary, one might think he is using it in the sense of being both logically (conceptually necessary) and metaphysically (causally necessary) necessary in relation to God with corruptible beings. I refer the reader to the above listed texts, and the note itself, in footnote 57.
 For the notion of a "corruptible thing" within God’s divine providence see (De veritate, 5.3).
 (Summa theologiae, Ia 49.2).
 See page one.
 I want to thank Fr. Dodds for pointing out the lack of clarity found in my first construction of this argument.
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