A subject of disputation in contemporary PoR literature is metaphysical rationalism, also known as explanatory universalism, that addresses the central question of whether metaphysical rationalism ostensibly yields strong Necessitarianism and has attested commendable reception as a modern yet acute rejoinder to unrestricted-PSR, namely the presupposition that every contingent proposition x must have a proposition y that explains x. Unrestricted-PSR as a rationalist principle, engineers many cosmological arguments, particularly arguments from contingency, because the principle underpins an essential premise: the impossibility of an infinite regress. However, the argument of Necessitarianism embraces this premise to attempt to dispute a common idea engineered by unrestricted-PSR: a conjunction of all contingent truths. While the argument has assumed many syllogistic forms, we will provide a general outline below:
Modal distinctions between hypothetical and metaphysical modal necessity among the essence of substances is a proposed idealized solution to affirm metaphysical rationalism in a theistic framework. For indeed, there is literature that has produced alternatives solutions on how rationalism can avoid necessitarianism, but such literature generally undermine an ultimate and fundamental level of explanation, a path more difficult for theism.
By: "kun"
However, this modal distinction of metaphysical modalities and hypothetical modalities is not progenitively Leibnizian, but is actually prevalent in the works of Ibn Sina. Ibn Sina writes,
"And if it does exist, it becomes necessary of existence by another thing; consequently it is something that is always possible of existence by itself and necessary of existence by another thing." (from ‘Uyun al-masa’il, in: (Bosley 1997, p14), cf. ibid. I.2.3).
Here, Ibn Sina demonstrates that a possible existent, can have dual modalities, that instantiate the essence in dual aspects and perspectives but nevertheless instantiate the same essence. The Necessary Existent, is one that is necessarily existent through itself, while the possible existent is one that is possible through itself (a substance whose essence is conceivable and coherent) yet necessary through another, a conceptual modal distinction between metaphysical modalities and hypothetical modalities.
The syllogism above, commences from the principle of contingent irreflexitivty which, more or less, mirrors some form of restricted-PSR. More precisley, contingent irreflexitivity is a principle made known by Peter Van Inwagen, which states that a contingent state of affairs cannot be wholly self-explanatory, namely that a contingent state of affairs cannot admit nor appeal to another contingent proposition, to explain that state of affairs. Generally, rudimentary theism depends on this principle, to assert a necessary being. However, it must be noted that the presupposition that a conjunction of all contingent truths can even be formed is one that is disputed by contemporary philosophers such as Graham Oppy (2006). However, for rudimentary theism, such a supposition is regularly postulated, as an infinite regress that is the set of all contingent members, and must logically terminate into an independent being. So what premise can we, at the very least, re-evaluate? Perhaps, we should consider the premise that directly yields Neccesitarianism, 'the conjunction of all contingent truths must be itself necessary since it admits to a necessary truth.' This is formally known as modal collapse, or when every true proposition is rendered necessarily true.
This can be seen in the classical works of Spinoza, who as an acclaimed Neccesitarian, accepted the conclusion that metaphysical rationalism yields a non-contingent world. The Spinozian paradigm contends that God is the only substance, something that is causally and conceptually self-contained. Hence, anything but God is a mode of God, something that is caused or conceived through the substance of God. Subsequently, modes and the effects begotten by the modes proceed from the causally and conceptually self-contained, which paradigmatically is the necessary substance of God. Therefore, modes and their effects, by modal collapse, are necessary.
Can metaphysical rationalism, then, escape the Spinozian paradigm? Leibniz's account of contingency based on per se possibility is something to consider. In the Leibnizian paradigm, per se possible substances are those substances whose essences are coherent and hence clearly conceivable hence there is no per se possible substance such that its essence cannot be clearly conceived on account of internal inconsistency. If the essence of a substance is what is responsible for the thinkability and conceivability of that substance, then it would be warranted to think that what makes something clearly conceivable would be clarity or consistency in the essence. So when Leibniz defines necessity as that the opposite of which cannot be clearly conceived, we may assume that he means that the opposite of something necessary does not have a coherent essence. For Leibniz as well as the majority of philosophers, a necessary being is a substance that necessarily exists. Similarly a possible existent is a substance that possibly exists. Presumably what Leibniz has in mind when he speaks of the contrary of a possible substance is not another substance but a proposition contrary to the proposition made true by the possible substance of the form “x possibly exists.” This proposition is of the form “it is not the case that x possibly exists.” To move even further Leibniz considers a substance as necessarily existent just in case it essentially exists and a substance as possibly existent just in case it is not essentially nonexistent. Leibniz believes that, with the sole exception of God, all truths about the existence or nonexistence of possible substances are contingent. Thus he seemingly believes that any substance with a coherent essence is not essentially nonexistent. Therefore, A substance is necessary just in case it exists essentially, meaning through itself. A substance is contingent just in case it exists but not essentially, meaning through another.
With this concise overview of the per se contingency, let's revisit P4: If the conjunction of all contingent truths is explained by a necessary truth, then the conjunction of all contingent truths must be itself necessary. By exploring per se possibility, we can argue that this premise is incoherent, since the premise implies that the conjunction of all contingent truths exist essentially meaning through itself. However we know, that the conjunction of all contingent truths exists through the necessarily true proposition y that explains the conjunction, henceforth a contradiction. How do we resolve this? For one, the modal language of this supposition is simply too obscure to discern the modal instantiations of 'necessary' in this premise. However, for this premise to be sound, we must employ a modal distinction, between the modal mode and the modal determination of the substance, a dual modality as one can refer to it. The modal determinator of the conjunction of all contingent truths is not essential, meaning the modal determinator is through another. Henceforth, if the conjunction of all contingent truths is necessary through another, ther other being 'true proposition y' then, by Leibnizian modal logic, the conjunction of all contingent truths is hypothetically necessary, yet metaphysically contingent, or contingent in themselves yet necessary through another. This modal distinction would ostensibly dissolve the contradiction because, the true proposition y that elucidates the conjunction is not hypothetically necessary , but metaphysically necessary, because the modal determinator of that proposition is not through another proposition but through the true proposition y. Henceforth, the syllogism yields a metaphysically necessary proposition y explaining a metaphysically contingent conjunction of all contingent truths xx's, thereby adhering to Contingent Irreflextivity and disproving P4. The conjunction of all contingent truths, C, is still necessary, but hypothetically necessary, a dual modality that instantiate the essence of the substance of C (of course, assuming that modalities are grounded in the essence) in dual aspects of the same substance.
P1. No contingent state of affairs can be wholly self-explanatory, all contingent state of affairs must admit to a necessary truth (Contingent Irreflextivity)
P2. Suppose there is a conjunction of all contingent truths xx's, that is explained by a true proposition y
P3. The conjunction of all contingent truths, must admit to a necessary truth.
P4. If the conjunction of all contingent truths is explained by a necessary truth, then the conjunction of all contingent truths must be itself necessary i.e wholly self-explanatory (Modal Collapse)
P5. P4 is a contradiction
P6. Therefore, there cannot be a conjunction of all contingent truths, i.e there are no contingent truths (Necessitarianism)