Aquinas's Second through Fifth Ways

         Considering a fully adequate discussion of Aquinas's Five Ways could occupy many more pages than what I plan to write just here, I will try to be reasonably succinct (though I think I have still failed in this) in my discussion of the Five Ways as a whole. Rather than providing an exhaustive description of each argument, I merely trace out what I consider a plausible way one might represent it. I then note points at which the argument would need either further support (which one might provide from other portions of Aquinas's work) or further development, owing to some difficulties that readers (especially contemporary ones) might find with them. None of these considerations are meant to be the final word (mine at least) on any one argument. With respect to giving a more detailed presentation of Aquinas's natural theology, I plan to enlarge on what I have written here sometime in the future. Following the same general scheme from my recent piece on the First Way, I will (in the future) try and describe the argument as accurately as I can, followed by a somewhat detailed assessment of it. So one might consider this a roadmap for future work that's subject to further revision and such. That is, nothing I say here is set in stone or even necessarily reflects my own thoughts on the rest of the Five Ways. I set my objections and everything else in place only tentatively. 

The Second Way

            One can, I think, represent Aquinas's Second Way in the following way:

First, assume that 

(NIR): for any series of efficient causes ordered per se, an infinite regress of causes is not possible.

Now,

(2.1) In the observable world there are series of causes ordered per se (premise).

(2.2) If something preceded itself, then it caused itself (premise).

(2.3) Necessarily, it is not possible that something caused itself (assumption).
(2.4) Necessarily, it is not possible that something preceded itself (2.2, 2.3 MP). 

(2.5) If a series is a series ordered per se, then any member earlier in the series causally affects an intermediate member and the intermediate member causally effects the final member (premise).  

(2.6) If one eliminates an earlier member in a series ordered per se, then one also eliminates the intermediate member and the final member (premise).

(2.7) Assume that there is a series ordered per se which has no first member (assumption).

(2.8) Therefore, there is a series ordered per se which has no final member (2.2-2.5, 2.6 MP).

(2.9) But this contradicts (2.5) (2.7 & 2.5).

(2.10) Therefore, there is a first cause (NIR, 2.1-2.9).

            In order to understand NIR, I need to say something about a series of efficient causes ordered per se versus a series of efficient causes ordered per accidens. Though Aquinas elaborates on the distinction somewhat in his Summa Contra Gentiles, a more detailed discussion of it is found in the writings of John Duns Scotus, Aquinas's near contemporary.

            In his own attempt at a proof for the existence of God, from his De Primo Principio, Scotus provides three criteria for distinguishing a series ordered per accidens versus a series ordered per se. To begin with the latter, a series ordered per se is (1) such that all the efficient causes in the series are either dependent (with respect to their causal efficacy) on the causes that precede them in the series, being first in the series in the sense of depending on no other causes in the series for their act of causing, or both are depended on and depend on other causes in the series. Second (2), in a series ordered per se, the type of causality of at least one of the efficient causes is of a higher type and rank, "inasmuch as the higher cause is more perfect." Scotus also argues that (2) is a consequence of (1) because no cause, in its exercise of its causal power, is essentially dependent on a cause of the same type as itself. The final difference (3) is that all of the efficient causes in a series ordered per se are simultaneously required for the series to have causal efficacy. In this last connection, Scotus is not explicit on whether he thinks (3) also follows in consequence of (1), but it seems he is on good grounds in claiming so. For, if the first cause in the series fails to exercise its causal efficacy precisely at the same time as the second cause is required to exercise its causal efficacy, it (the second cause) will have no causal efficacy with respect to what it requires for bringing about its effect.

            The staple medieval example of a series ordered per se is a hand's moving a staff to move a stone. In keeping with (2), the hand is a higher type of cause from the staff because the hand (or, more accurately, the mind controlling the hand) can (in some sense at least) by itself initiate movement or causal activity in the series, whereas the staff cannot. Since the staff depends on the hand precisely in the staff's act of causing, moreover, the example also satisfies (1). Finally, arriving at (3), the staff and the hand must exercise their causal activity at the same time, and therefore must both be present such that the hand can act with the staff. The relations that obtain in virtue of (1) and (2), one might note, are asymmetrical: if a causes b to act, it does not follow that b causes a to act. They are also transitive: because if a causes b to act and b causes c to act, it also follows that a causes c to act. One might object to the claim that the relations that obtain between a and b in virtue of (1) and (2) are that of asymmetry and transivity, on the basis that a is also dependent on b in a's act of causing. My reply is that this response succeeds only if one equivocates between a and b in the sense of (1) and (2), on the one hand, and, on the other hand, a and b in the distinct sense implied by the relations that obtain between a and b in virtue of (3). For the relation between a and b in sense (3) is indeed symmetrical, and in this third sense it is true both that b depends on a and that a depends on b. But this sense, I hope is clear, is perfectly distinct from that logically implied by senses (1) and (2).

            In contrast to a series of efficient causes ordered per se, on the other hand, there is also a series of efficient causes ordered per accidens. Having defined a series ordered per se in terms of (1) through (3), a simple and clear way of explaining a series ordered per accidens is as merely a series in which (1) through (3) do not obtain. The standard example here is that of Abraham's begetting Isaac and Isaac's begetting Jacob. As his existence is concerned, so the example goes, Isaac depends on Abraham's having begotten him some time in the past. As it concerns his act of begetting Jacob, however, Isaac does not, in any active sense, depend on Abraham. He can act so to beget Jacob even if Abraham is no longer alive.

            Each member that is part of a series of efficient causes ordered per accidens, therefore, is independent of any prior member so far as its causal efficacy is concerned. In consequence, the time that separates each act of causality in the series is also irrelevant insofar as each agent's causal efficacy is concerned. That is, the causes need not exist simultaneously for the series as a whole to have its causal efficacy. For this reason, then, it is possible that a series of causes ordered per accidens stretch back infinitely into the past.

            Now, returning to Aquinas's argument, if a series ordered per se is such that it has feature (1) necessarily, and if features (2) and (3) follow from (1), NIR will also seem true. Assuming that this is right, Aquinas will still have to show that the first premise of the argument is true, i.e., that there really are, in the world, series ordered per se. One thing going for him in this regard is that it seems that there are such series if the example of the hand moving the staff's moving the stone really does have all three features Scotus (and Aquinas) assign to it. Whether this is indeed true is an interesting question, but I postpone it because my discussion of the second way has already gone on long enough.  

Third Way

(3.1) Some things are contingent (assumption).

(3.2) If something is contingent, then it can possibly not exist (true by definition).

(3.3) If something can possibly not exist, then there is a time when it does not exist (premise).

(3.4) If everything can possibly not exist, then there is a time when nothing exists (premise).

(3.5) If there is a time when nothing exists, then nothing now exists (premise).

(3.6) But something now exists (assumption).

(3.7) There are some things that necessarily exist (2.5 and 2.4 MT).

(3.8) If something necessarily exists, then either it has its necessary existence from another or from itself (2.7 & LEM).

(3.9) If it receives its necessity from another, then this process cannot continue forever (premise).

(3.10) Therefore, there is a necessary being that has its necessity from itself.

            As it stands, the argument is not obviously valid. (4) seems to make an illicit jump from (3) insofar as it is not obvious that Aquinas is entitled to "there is a time when everything does not exist" rather than something like "every 'thing' has a time when it does not exist." But perhaps the move is more plausible than it looks. For, if one takes Aquinas's mention of generation and corruption into the picture, one might argue as follows. If one grants (3) on the basis that if something is such that, in sometime in its existence, it is generated or it is corrupted, then there is a time when it does not exist. But if it is never generated or corrupted, it is not possible (in the sense of generation and corruption) for it not to exist, so it is necessary. To save (4), however, one would seem to need a further premise. One might assume, for example, that the universe is infinite in age, in which case, if it is possible that everything goes out of existence, there will be (at least one might argue) some time when that possibility is realized. And if there was ever a time when nothing existed in the past, it seems plausible to conclude that nothing exists now (which is absurd). This having been granted, one might also grant that the argument is valid. However, even now, it is not obvious that premise (9) is true. Why cannot this series extend backwards infinitely? And Aquinas does not seem to offer justification for it. Moreover, even if one grants that the move from (3) to (4) on the basis of the new (suppressed) premise follows logically, one may doubt whether it is true. For it seems plausible to me that if it is possible for everything to go out of existence that this possibility will be sometime realized. But I cannot think of anything really convincing to say against someone who simply denies this.

Fourth Way

(4.1) Some things are found to be better, truer, more excellent than others (i.e., are great-making properties) (assumption).

(4.2) If some things are found to be better, truer, etc. than others, then such comparative terms describe varying degrees of approximation to a superlative (premise).

(4.3) If such comparative terms describe varying degrees of approximation to a superlative, then there is (in the sense of existence) a superlative to which these comparative terms correspond (premise).

(4.4) 'Being' or 'existence' is a comparative term in the sense of (4.2) (premise).

(4.5) There is something that is a 'being' in the sense of a superlative to which these comparative terms correspond (4.4 & 4.2 - 4.3 MP).

(4.6) If many things possess a great-making property in common, then the thing most fully possessing it causes it in the others (premise).

(4.7) Therefore, there is something that causes in all other things their being, their goodness, and whatever  they have (4.1 - 4.5, 4.6 MP).

            Assuming that the argument is valid, one might first try to question the move from (4.2) to (4.3). If there is something that possesses a perfection to some arbitrary but finite degree, it seems possible that there is something that possesses it to an ever slightly higher degree. And it seems possible that one could continue this process indefinitely, without ever arriving at a superlative thing that possesses the perfection to a maximum degree. Discounting this possibility, it is not clear that from (4.3), (4.5), and (4.6), Aquinas is entitled to (4.7), because the only relevant perfection he has claimed the superlative being possesses is superlative or maximal existence. But this might not matter so much, considering that if one grants (4.1,), (4.5), and (4.6), one concedes that there is a being that causes being in all other beings, and this seems all he needs. One last possibility worth considering is that Aquinas's opponent would likely move to block (4.4), since there is not an obvious sense in which something possesses being to a greater degree than another. It does not, the complaint might go, even make sense to say that I exist to a greater degree than this desk.   

Fifth Way

(5.1) Some bodies in nature do not hit their goals by accident (assumption).

(5.2) If bodies in nature do not hit their goals by accident, then they hardly ever vary in their behavior (premise).

(5.3) Some bodies in nature that act for an end/goal lack awareness (assumption).

(5.4) If anything lacks awareness, then either its behavior is guided by an agent with awareness or it hits its goals by accident (premise).

(5.5) If anything hits its goals/ends by accident, then it is not the case that it hardly ever varies in its behavior (premise).

(5.6) But (5.5) is false (5.5 & 5.2 MT).  

(5.7) Therefore, its behavior is guided by an agent with awareness (5.1 - 5.3 & 5.5, (5.4 MP & (5.6 & 5.4))).

            Assuming once more that this argument is valid, the remaining consideration is to consider the truth of its premises. (5.2) may seem controversial, but one need only read it as claiming that if some bodies in nature do not act merely by coincidence, then they produce certain effects in such a way that their production of these effects hardly ever varies. It is the apparent nature of copper, for example, always to dissolve in acid; and, correlatively, it is the apparent nature of acid always to dissolve copper. (5.1) is more controversial, insisting as it does that something that hardly ever varies in its production of a certain effect does not, qua its production of the said effect, produces its effect by merely a coincidence. (5.3) seems obvious). (5.4.) seems intuitively plausible, but one might protest that it does not exhaust the possibilities for the production of seemingly ordered effects in nature. (5.5) is merely the negation of (5.1), and anyone who has difficulty accepting (5.1) will likely have similar difficulties with (5.5).