This is the weekly Q & A blog post by our Research Professor in Philosophy, Dr. William Lane Craig.


Dear Dr. Craig,

First, I just want to say thank you very much for all of the work you are doing. It has been a great help to me in my life as a Christian and God has truly used you to strengthen my faith. We actually met recently at your Defenders Class when I came to visit Atlanta the weekend you had laryngitis. It was a privilege to briefly speak with you and I'm glad you are feeling better! That being said, I have a couple questions concerning the attributes of necessity and aseity, particularly with how they play into the Leibnizian Cosmological Argument (hereafter LCA). I find this argument extremely compelling, but I would like clarification on an essential aspect of it. On question of the week 190, you make it clear that in the context of your formulation of the LCA, you are not using necessity and contingency in the broadly logical sense. Rather, you are using them to refer to beings which exist by a necessity of their own nature and beings which depend on external causes for their being. Thus, on this analysis, a logically necessary being is considered contingent if it depends upon another logically necessary being for its existence (such as in Absolute Creationism or Conceptualism with respect to abstract objects for example). What sort of modality is this though? In looking through material on modality, I haven't been able to find a term for the type of modality used here. In Philosophical Foundations for a Christian Worldview, you preface this definition of necessary beings and contingent beings by saying "On this analysis." Is this suggesting that the use of the words necessary and contingent in this context are peculiar to this argument?

Furthermore, I can't help but notice several places in the argument though where it seems to use contingency and necessity in the broadly logical sense, and not in the sense defined in the argument. One example is when you deal with the objection from Bede Rundle that, while no being exists necessarily, it is necessary that some contingent being or another exists. You point out that this amounts to a denial of the principle of sufficient reason, and that it postulates the existence of brute contingents in every possible world. This seems to be using a broadly logical sense of necessity and contingency, rather than the one described above. Also, in the context of discussing the contingency of the universe, you appeal to our intuition of a possible world with no concrete objects and a possible world in which a different set of fundamental particles exist in order to establish the universe's contingency. This also seems to be using a logical sense of modality, since it seems to identify contingency with existing in some but not all possible worlds, and not merely being dependent on external causes for a things existence. No doubt a logically contingent being will be contingent in the sense described by the argument, but are these words being used univocally throughout the argument?

In reflecting on your writings on divine aseity though, it occurred to me that the types of beings described on your version of the PSR are very close to the concepts of beings which exist a se and beings which exist ab alio. If I understand aseity correctly, it is the property of self-existence and independence from any other external beings or causes. That sounds a lot to me like a being which exists by a necessity of its own nature. In your article "Timothy O'Connor on Contingency: A Review on Theism and Ultimate Explanation: The Necessary Shape of Contingency," you say "It needs to be kept in mind that when O'Connor speaks of a necessary being, he means a being which exists not only necessarily but a se (p. 155, n. 7), so that beings that are necessary ab alio do not enter the picture." Does this suggest that the necessary beings of your version of the argument are to be identified with beings which are logically necessary a se and that contingent beings are to be identified as both logically contingent beings (which exist ab alio) and beings which are logically necessary ab alio, or am I misunderstanding concepts here? And if that is the case, do you think that the argument should be rephrased either in terms of aseity or in terms of broadly logical modality which is qualified by whether or not the being exists a se or ab alio?

Thank you so much for considering my question and God bless!


United States

Dr. William Lane Craig’s Response

Dr. William Lane Craig

Thank you for this most intelligent question, Matt! I’m glad that you were able to visit us in Defenders class.

For those who lack your background, let’s get the Leibnizian cosmological argument on the table here:

1. Everything that exists has an explanation of its existence (either in the necessity of its own nature or in an external cause).
2. If the universe has an explanation of its existence, that explanation is God.
3. The universe exists.
4. Therefore, the universe has an explanation of its existence.
5. Therefore, the explanation of the existence of the universe is God.

Like you, I find this argument to be very powerful.

Now your question concerns how the properties of necessity and aseity feature in this argument. As you rightly observe, a being that existed in every broadly logically possible world would exist necessarily, but if it has a cause, then it doesn’t exist by a necessity of its own nature. Paradoxically, it exists necessarily but contingently. I say “paradoxically” because there is no contradiction here. By “contingently” in this context one means “dependently.” Absolute creationists, for example, would say that mathematical objects exist in this way: they are created by God in every possible world and so exist necessarily, even though they depend upon God for their existence. They exist necessarily, but they are not self-existent.

Now your first question concerns the kind of modality at stake here. This distinction between necessary existence and self-existence is one that usually arises in a theistic context and has been remarked on by other theists. There is no standard terminology for this kind of modality. But interestingly, medieval thinkers like Thomas Aquinas did distinguish between something that is “necessary of itself” (per se necessarium) and something that has “a cause of its necessity in another” (causam suae necessitatis aliunde) (Summa theologiae 1.2.3). Modal metaphysics today needs some such categories to do justice, not just to this argument, but, as the cases of absolute creationism and conceptualism also illustrate, to the subtleties involved in doing modal metaphysics.

Now when you recall that necessity per se (to borrow Thomas’ terminology) entails plain old necessity, you can see that if a being does not even have necessity, then it doesn’t have necessity per se either! So when Bede Rundle claims that there are contingent beings in every world but no necessary being, he’s using “necessary” and “contingent” in the usual sense, and it’s fine to point out that on his view there is no explanation for why these contingent beings exist.

Similarly, if I can show that the universe does not exist even necessarily, then it certainly does not exist necessarily per se either. That is, if one can show that the universe exists contingently in a broadly logical sense, then it certainly does not exist necessarily per se.

I wholeheartedly concur with you that the distinction we are trying to draw is synonymous with the distinction between something’s existing a se (in or of itself) versus existing ab alio (through another). (Again, we can thank the medievals for this terminology.) So you’re right on target in identifying a being which exists by a necessity of its own nature with a being that has the property of aseity--which happens to be the subject of my current research! So you are right in saying that premiss (1) of the Leibnizian argument distinguishes between two sorts of beings: those that are self-existent (have existence a se) and those that exist through another (have existence ab alio). Those things that exist ab alio might exist broadly logically contingently (in only some possible worlds) or broadly logically necessarily (in all possible worlds):

I. Existence a se
II. Existence ab alio

A. Broadly logically contingent existence
B. Broadly logically necessary existence

So do I “think that the argument should be rephrased either in terms of aseity or in terms of broadly logical modality which is qualified by whether or not the being exists a se or ab alio?” No; the argument is hard enough as it is for people to understand, and introducing such terminology would only serve to make it more confusing. Better to make such clarifications for the cognoscendi in a Question of the Week!

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