Strong vs Weak necessitarianism

Examining the Plausibility and Consequences of Necessity

Is necessitarianism really as implausible as most philosophers tend to believe? I say it depends on what we mean by necessitarianism. Dr. Morvarid, in his excellent paper Strong vs Weak Necessitarianism: An Avicennian Defense of The Principle of Sufficient Reason, outlines the distinction between strong and weak necessitarianism. The former is the thesis that for any existent, F, F is either necessary in itself or through another. The latter, simply put, is the thesis that every existent is necessary in itself.

You may be wondering what “necessary in itself” and “necessary through another” mean. An existent is necessary in itself iff (if and only if) its essence guarentees its existence. In other words, its essence includes existence. By contrast, an existent is necessary through another iff its existence is additional to its essence, i.e., its essence does not guarantee its existence. (It is crucial to note that the notion of essence at play here is not the modal notion of essence, which is defined in terms of metaphysical necessity. Otherwise, the distinction between “necessary in itself” and “necessary through another” would collapse, as both are metaphysically necessary. Instead, the notion of essence at work here is the Aristotelian notion of essence.)

Now that I've clarified some terminology, I aim to show that, when philosophers think about the implausibility of necessitarianism, they usually have strong necessitarianism (SN) in mind. If SN is true, then every existent could not fail to exist; this is because every existent’s essence would include its existence. I, sharing the intuition of many philosophers, take this position to be highly implausible. Surely, there are at least some things that, when considered in themselves, can fail to exist (e.g., chairs, tables, etc.). There is nothing about the essence of a table, for example, that guarantees its existence. It's no wonder then that we observe tables coming to exist after previously not existing and vice-versa. If we accept SN, however, the notion of a table coming to exist after previously not existing would be nonsensical, since its essence includes its existence, and thus it would exist essentially. It's clear that what is entailed by SN is inconsistent with what we experience in reality, and that is a strong reason to reject SN.

Weak necessitarianism (WN) does not, I believe, suffer the same problems as SN and is not nearly as implausible, at least not evidently so. Let us assume that WN is true and consider some existent, F, that is necessary through another. Since F is necessary through another, it follows that F’s existence is additional to its essence, and, therefore, it must be necessitated by some existent other than itself. Given that F is necessitated, it follows that F, in relation to its cause, could not have been otherwise. Is this view really implausible? I don't think so. In fact, I believe it's plausible. To deny the plausibility of WN is tantamount to denying the implausibility of an effect not obtaining despite the presence of its complete cause, i.e., the cause that necessitates its effect by virtue of including all the necessary conditions for it. To illustrate this point with an example, imagine a billiard ball in motion coming into contact with another stationary billiard ball, which then begins to move due to the contact of the first with the second ball. A cool GIF representation of the example is provided below.

The motion of the second ball (effect) is due to its complete cause. Moreover, as I've already mentioned, the complete cause includes all the necessary conditions of the effect and necessitates it. Now, ask yourself: is it plausible that the effect does not occur despite the presence of all the necessary conditions (e.g., the air resistance, the friction of the table, the particular speed and position, etc.)? I think not. There wouldn't be a reason, unless the cause was different, why the effect does not obtain. One may object that the effect can be distinct despite the presence of its complete cause. The issue with this objection is that, assuming that the effect can truly be distinct, it follows that the distinction isn't explained by the complete cause. In other words, the distinction is simply a brute fact, which is unacceptable under necessitarianism.

Peter Van Inwagen once famously argued that the PSR entails necessitarianism. The power of the argument put pressure on philosophers to either deny the PSR or accept necessitarianism. It's safe to say that the majority chose the former. However, if I am right regarding the plausibility of WN, then one need not deny necessitarianism simpliciter; rather, one only needs to deny SN.