Craig distinguishes three types of cosmological arguments. The first, advocated by Aquinas, is based on the impossibility of an essentially ordered infinite regress. The second, which Craig terms the kalām argument, holds that an infinite temporal regress is impossible because an actual infinite is impossible. The third, espoused by Leibniz and Clarke, is overtly founded on the Principle of Sufficient Reason (Craig 1980, 282). Another way of distinguishing between versions of the argument is in terms of the relevance of time. In Aquinas's version, consideration of the essential ordering of the causes or reasons proceeds independent of temporal concerns. The relationship between cause and effect is treated as real but not temporal, so that the first cause is not a first cause in time but a sustaining cause. In the kalām version, however, the temporal ordering of the causal sequence is central. The distinction between these types of argument is important because the objections raised against one version may be irrelevant to the other versions. So, for example, a critique of a particular version of the Principle of Sufficient Reason (PSR), which one finds developed by William Rowe or Richard Gale, might not be telling against the Thomistic or kalām versions of the argument.
Thomas Aquinas held that among the things whose existence needs explanation are contingent beings that depend for their existence upon other beings. Richard Taylor (1992, 99–108) discusses the argument in terms of the universe (meaning everything that ever existed) being contingent and thus needing explanation. Arguing that the term “universe” refers to an abstract entity or set, William Rowe rephrases the issue,“Why does that set (the universe) have the members that it does rather than some other members or none at all?” (Rowe 1975, 136). Or, why is there anything at all? (Smart, in Haldane and Smart, 35; Rundle). The response of the cosmological argument is that what is contingent exists because of the action of a necessary being.
The cosmological argument begins with a fact about experience, namely, that something contingent exists. We might sketch out the argument as follows.
A contingent being (a being such that if it exists it could have not-existed or could cease to) exists.
Therefore, a necessary being (a being such that if it exists cannot not-exist) exists.
Over the centuries philosophers have suggested various instantiations for the contingent being noted in premise 1. In his Summa Theologica I, q. 2, a 3, Aquinas argued that we need a causal explanation for things in motion, things that are caused, and contingent beings. Others, such as Richard Taylor and Richard Swinburne (1979), propose that the contingent being referred to in premise 1 is the universe. The connection between the two is supplied by John Duns Scotus, who argued that even if the essentially ordered causes were infinite, “the whole series of effects would be dependent upon some prior cause” (Scotus, 46). Whereas the contingency of particular existents is generally undisputed, the contingency of the universe deserves some defense (see 3.2). Premise 2 invokes a version of the Principle of Causation or the Principle of Sufficient Reason; if something is contingent, there must be a cause of its existence or a reason or explanation why it exists rather than not exists. The point of 3 is simply that something cannot cause its own existence, for this would require it to already be (in a logical if not a temporal sense). Premise 4 is true by virtue of the Principle of Excluded Middle: what explains the existence of the contingent being either are solely other contingent beings or includes a non-contingent (necessary) being. Conclusions 6 and 7 follow validly from the respective premises.
For many critics, premise 5 holds the key to the argument's success or failure. Whether 5 is true depends upon the requirements for an adequate explanation. According to the Principle of Sufficient Reason (PSR), what is required is an account in terms of sufficient conditions that provides an explanation why the cause had the effect it did, or alternatively, why this particular effect and not another arose. Swinburne (1979, 72–77), and Alexander Pruss (2006, 16–18) after him, note diverse kinds of explanations. A full explanation provides the cause together with the reason that necessitated the effect or what happened; it is “a set of factors that together are sufficient for the occurrence of an event” (Swinburne 1979, 24, 73). “It does not allow a puzzling aspect of the explanandum to disappear: anything puzzling in the explanandum is either also found in the explanans or else explained by the explanans” (Pruss 2006, 17). In a complete explanation, every aspect of the explanandum and explanans at the time the occurrence is accounted for; nothing puzzling remains. Pruss and Swinburne argue that the kind of explanation required by the PSR is a complete explanation.
Quinn argues that an adequate explanation need not provide a complete explanation (584–85); a partial explanation might do just as well, depending on the context. Among these adequate explanations of why this actual world obtains rather than another possible world (including one with no contingent beings) is that the universe is an inexplicable brute fact and that God strongly actualized the world (although not everything in it). He refuses to take sides on the debate between explanations, except to say that science cannot provide an adequate explanation if the explanatory chain is infinite, for the chain of causes is itself contingent or it ends in an initial contingency not scientifically accountable. However, not only does Quinn not clarify what constitutes an adequate explanation, but as Pruss contends, the PSR “is not compatible with an infinite chain of explanations that has no ultimate explanans,” for in an infinite chain something puzzling remains to be explained, with the result that the PSR would again be invoked to explain what is puzzling. More than a scientific explanation is required to provide the complete explanation required by the PSR.
One worry with understanding the PSR is that it may lead to a deterministic account that not only bodes ill for the success of the argument but on a libertarian account may be incompatible with the contention that God created freely. Pruss, however, envisions no such difficulty. “What gives sufficiency to explanation is that mystery is taken away, for example, through the citing of relevant reasons, not that probability is increased” (Pruss, 2006, 157). Giving reasons neither makes the event deterministic nor removes freedom. “Once we have said that x freely chose A forR, then the only thing left that is unexplained is why x existed and was both free and attracted byR” (158).
Finally, it should be noted in 7 that if the contingent being identified in 1 is the universe, the necessary being cannot provide a natural explanation for it, for we know of no natural, non-contingent causes and laws or principles from which the existence of the universe follows. What is required is a personal explanation in terms of the intentional acts of some eternal supernatural being. Since the argument proceeds independent of temporal considerations, the argument does not propose a first cause in time, but rather a first or primary sustaining cause of the universe. As Aquinas noted, the philosophical arguments for God's existence as first cause are compatible with the eternity of the universe (On the Eternity of the World).
The question whether the necessary being to which the argument concludes is God is debated. Some hold that the assertion that the first sustaining cause is God is not part of the cosmological argument per se; such defenders of the argument sometimes create additional arguments to identify the first cause. Others, however, contend that from the concept of a necessary being other properties appropriate to a divine being flow. O'Connor (2005) argues that being a necessary being cannot be a derivative emergent property, otherwise the being would be contingent. Likewise the connection between the essential properties must be necessary. Hence, the universe cannot be the necessary being since it is mereologically complex. Similarly, the myriad elementary particles cannot be necessary beings either, for their distinguishing distributions are externally caused and hence contingent. Rather, he contends that a more viable account of the necessary being is as a purposive agent with desires, intentions, and beliefs, whose activity is guided but not determined by its goals, a view consistent with identifying the necessary being as God. Koons also is willing to identify the necessary being as God, constructing corollaries regarding God's nature that follow from his construction of the cosmological argument. Oppy (1999), on the other hand, expresses skepticism about the possibility of such a deductive move.
Interpreting the contingent being in premise 1 as the universe, Bertrand Russell denies that the universe needs an explanation; it just is. Russell, following Hume (1980), contends that since we derive the concept of cause from our observation of particular things, we cannot ask about the cause of something like the universe that we cannot experience. The universe is “just there, and that's all” (Russell, 175).
But we don't need to experience every possible referent of the class of contingent things to be able to conclude that a contingent thing needs a cause. “To know that a rubber ball dropped on a Tuesday in Waggener Hall by a redheaded tuba player will fall to the ground,” I don't need a sample that includes tuba players dropping rubber balls at this location (Koons 1997, 202). Similarly, one does not need to experience a contingent cosmos to know it is caused.
Russell correctly notes that arguments of the part-whole type can commit the Fallacy of Composition. For example, the argument that since all the bricks in the wall are small, the wall is small, is fallacious. Yet it is an informal fallacy of content, not a formal fallacy. Sometimes the totality has the same quality as the parts because of the nature of the parts invoked—the wall is brick because it is built of bricks. The universe's contingency, theists argue, resembles the second case. If all the contingent things in the universe, including matter and energy, ceased to exist simultaneously, the universe itself, as the totality of these things, would cease to exist. But if the universe can cease to exist, it is contingent and requires an explanation for its existence (Reichenbach, chap. 5).
Rowe's example, however, fails, for it is possible that all the horses break a leg and none finishes the race. That is, the necessity that some horse will win follows only if there is some reason to think that some horse must finish the race. Similarly, his objection to the universe's contingency will hold only if there is some reason to think that the existence of something is necessary. One argument given in defense of this thesis is that the existence of one contingent being may be necessary for the nonexistence of some other contingent being. But though the fact that something's existence is necessary for the existence of something else holds for certain properties (for example, the existence of children is necessary for someone to be a parent), it is doubtful that something's existence is necessary for something else's nonexistence per se, which is what is needed to support the argument that denies the contingency of the universe. Hence, given the contingency of everything in the universe, it remains that there is a possible world without any contingent beings.
Whether this argument for the contingency of the universe is similar to that advanced by Aquinas in the Third Way depends on how one interprets Aquinas's argument. Aquinas holds that “if everything can not be, then at one time there was nothing in existence.” Plantinga, among others, points out that this may commit a quantifier mistake, for the reason noted above (Plantinga, 6; Kenny, 56–66). However, Haldane (Smart and Haldane, 132) defends the cogency of Aquinas's reasoning on the grounds that Aquinas's argument is fallacious only on a temporal reading, but Aquinas's argument employs an atemporal ordering of contingent beings. That is, Aquinas does not hold that over time there would be nothing, but that in the per se ordering of causes, if every contingent thing in that order did not exist, there would be nothing.
To avoid any hint of the Fallacy of Composition and to avoid these complications, Koons (198–99) formulates the argument for the contingency of the universe as a mereological argument. If something is contingent, it contains a contingent part. The whole and part overlap and, by virtue of overlapping, have a common part. Since the part in virtue of which they overlap is wholly contingent, the whole likewise must be contingent.
Rowe (1975, 166) develops a different argument to support the thesis that the universe must be contingent. He argues that it is necessary that if God exists, then it is possible that no dependent beings exist. Since it is possible that God exists, it is possible that it is possible that no dependent beings exist. (This conclusion is licensed by the following modal principle: If it is necessary that if p then q, then if it is possible that p, it is possible that q.) Hence, it is possible that there are no dependent beings; that is, that the universe is contingent. Rowe takes the conditional as necessarily true in virtue of the classical concept of God, according to which God is free to decide whether or not to create dependent beings.
Pruss (1999) takes what Rowe (1975) calls the Hume-Edwards principle to task. An explanation of the parts may provide a partial but not a complete explanation. The explanation in terms of parts may fail to explain why these parts exist rather than others, why they exist rather than not, or why the parts are arranged as they are. Each member or part will be explained either in terms of itself or in terms of something else that is contingent. The former would make them necessary, not contingent, beings. If they are explained in terms of something else, they still remain unaccounted for, since the explanation would invoke either an infinite regress of causes or a circular explanation. Pruss employs the chicken/egg sequence: chickens account for eggs, which account for chickens, and so on where the two are paired. But appealing to an infinite chicken/egg regress or else arguing in a circle explains neither any given chicken nor egg.
When the existence of each member of a collection is explained by reference to some other member of that very same collection then it does not follow that the collection itself has an explanation. For it is one thing for there to be an explanation of the existence of each dependent being and quite another thing for there to be an explanation of why there are dependent beings at all (Rowe 1975, 264).
Interestingly enough, this approach was anticipated by Aquinas in his third way in his Summa Theologica (I,q.2,a.3). Once Aquinas concludes that necessary beings exist, he then goes on to ask whether these beings have their existence from themselves or from another. If from another, then we have an unsatisfactory infinite regress of explanations. Hence, there must be something whose necessity is uncaused. As Kenny points out, Aquinas understands this necessity in terms of being unable to cease to exist (Kenny, 48). Although Aquinas understands the uncaused necessary being to be God, Rundle takes this to be matter-energy itself. Since Rundle's objection introduces the notion of causation in time, it is more appropriate to the kalām argument. We will return to this issue in section 5, when we consider that argument.
Finally, Richard Swinburne asks how far any explanation must go. Whereas traditional cosmological arguments contend that we need to explain the existence of every relevant contingent causal condition in order to explain another's existence (Scotus's ordering of per secauses), Swinburne terms this requirement the completist fallacy (1979, 73). Swinburne notes that an explanation is complete when “any attempt to go beyond the factors which we have would result in no gain of explanatory power or prior probability” (1979, 86). But explaining why something exists rather than something else or than nothing and why it is as it is gives additional explanatory power in explaining why a universe exists at all. Gale (1991, 257–8) concludes from this that if we are to explain the parts of the universe and their particular concatenation, we must appeal to something other than those parts.
Critics of the argument contend that the Causal Principle or, where applicable, the PSR, that underlies versions of the argument is suspect. As Hume argued, there is no reason for thinking that the Causal Principle is true a priori, for we can conceive of effects without conceiving of their being caused and what is conceivable is possible in reality (1993, IV). Neither can an argument for the application of the Causal Principle to the universe be drawn from inductive experience. Even if the Causal Principle applies to events in the world, we cannot extrapolate from the way the world works to the world as a whole (Mackie, 85).
Several replies are in order. First, Hume's conceivability to possibility argument is unsound. For one thing, whose conceivability is being appealed to here? Someone who fails to understand a necessarily true proposition might conceive of it being false, but from this it does not follow that it possibly is false. For another, in the phenomenology of conceivability, what is really conceivable is difficult if not impossible to differentiate from what some might think is conceivable. And even if something is conceivable, say in a logical sense, it does not follow that it is metaphysically or factually possible. Hence, the argument based on conceivability is suspect.
Second, there is reason to think that these principles are true. Some suggest a pragmatic-type of argument: the principles are necessary to make the universe intelligible (Taylor). Critics reply that the principles then only have methodological or practical and not ontological justification. As Mackie argues, we have no right to assume that the universe complies with our intellectual preferences for causal order. We can simply work with brute facts. Perhaps so, but without such principles, science itself would be undercut; as Pruss (2006, 255) points out, “Claiming to be a brute fact should be a last resort. It would undercut the practice of science.” Utilization of the principles best accounts for the success of science, and indeed, for any investigatory endeavor (Koons). The best explanation of the success of science and other such rational endeavors is that the principles are really indicative of how reality operates.
Some have gone further to suggest that the PSR in particular is “self-evident, obvious, intuitively clear, in no need of argumentative support” (Pruss 2006, 189). For example, Pruss holds the principle to be self-evident in the sense that anyone who understands it correctly understands that it is true. They might not know it to be self-evidently true, but they do understand it to be true. This is consistent with persons denying it is self-evident, for those who deny it might misunderstand the principle in various ways. They might experience a conceptual blindness to the nature of contingency or they might be “talked out of” understanding the principle because of its controversial implications (e.g., the existence of a necessary being).
The problem with self-evidence is that, in contrast to analyticity, it is in relation to the knowers themselves, and here diversity of intuitions varies, perhaps according to philosophical or other types of perspectives. But if the principles truly are self-evident, it would be strange to respond to skeptics by attempting to give reasons to support that contention, and were such demanded, the request would itself invoke the very principles in question.
Clearly, the soundness of the deductive version of the cosmological argument hinges on whether principles such as that of Causation or Sufficient Reason are more than methodologically true and on the extent to which these principles can be applied. Critics of the argument will be skeptical, seeing what such acceptance will commit themselves to. Defenders of the argument will contend that judging the principles by the outcome of their application begs the question against them and, indeed, to require a sufficient reason to establish their truth begs the question at hand.
Immanuel Kant objected to the use of “necessary being” throughout the cosmological argument, and hence to the conclusion that a necessary being exists. Kant held that the cosmological argument, in concluding to the existence of an absolutely necessary being, attempts to prove the existence of a being whose nonexistence “is impossible,” is “absolutely inconceivable” (B621). Kant indicates that what he has in mind by an “absolutely necessary being” is a being whose existence is logically necessary, where to deny its existence is contradictory. The only being that meets this condition is the most real or maximally excellent being — a being with all perfections, including existence. This concept lies at the heart of the ontological argument. Although in the ontological argument the perfect being is determined to exist through its own concept, in fact nothing can be determined to exist in this manner; one has to begin with existence. In short, the cosmological argument presupposes the cogency of the ontological argument. But since the ontological argument is defective for the above (and other) reason, the cosmological argument that depends on or invokes it likewise must be defective (Kant, B634).
And by “a necessary being” the cosmological argument means “a logically necessary being,” i.e. “a being whose non-existence is inconceivable in the sort of way that a triangle's having four sides is inconceivable”....Now since “necessary” is a word which applies primarily to propositions, we shall have to interpret “God is a necessary being” as “The proposition ‘God exists’ is logically necessary” (in Flew and MacIntyre, eds., New Essays in Philosophical Theology, 37).
(In a later work Smart (41–47) broadened his notion of necessity.) One still finds remnants of this in the contention that speaking about necessary beings does not differ from speaking of the necessity of propositions (see the Gale-Pruss argument below).
Many recent discussions of the cosmological argument, both supporting and critiquing it, interpret the notion of a necessary being as a being that cannot not exist. It is a being that exists in all possible worlds. As such, as Plantinga notes, if a necessary being is possible, it exists (God, Freedom and Evil, 110). The only question that remains is whether God's existence is possible. This notion is similar to, if not a modernization of, Aquinas's contention that God's essence is to exist. Aquinas attempts to avoid the accusation that this invokes the ontological argument on the grounds that we do not have an adequate concept of God's essence. However, if we understand “necessary being” in this sense, we can dispose of the cosmological argument as irrelevant; what is needed rather is an argument to establish that God's existence is possible, for if it is possible that it is necessary that God exists, then God exists (by Axiom S5).
But this need not be the sense in which “necessary being” is understood in the cosmological argument. A more adequate notion of necessary being is that the necessity is metaphysical or factual. A necessary being is one that if it exists, it neither came into existence nor can cease to exist, and correspondingly, if it does not exist, it cannot come into existence (Reichenbach, 117–20). If it exists, it eternally maintains its own existence; it is self-sufficient and self-sustaining. So understood, the cosmological argument does not rely on notions central to the ontological argument. Rather, instead of being superfluous, the cosmological argument gives us reason to think that the necessary being exists rather than not.
Mackie replies that if God has metaphysical necessity, God's existence is contingent, such that some reason is required for God's own existence (Mackie, 84). That is, if God necessarily exists in the sense that if he exists, he exists in all possible worlds, it remains logically possible that God does not exist in any (and all) possible worlds. Hence, God is a logically contingent being and so could have not-existed. Why, then, does God exist? The PSR can be applied to the necessary being.
The theist responds that the PSR does not address logical contingency, but metaphysical contingency. One is not required to find a reason for what is not metaphysically contingent. It is not that the necessary being is self-explanatory; rather, a demand for explaining its existence is inappropriate. Hence, the theist concludes, Hawking's question “Who created God?” (Hawking, 174) is out of place (Davis).