In a paper I read recently, the author claims that metaphysical theories such as Determinism or Materialism/Physicalism may be regarded as contingent truths. I take Determinism and Materialism/Physicalism to be prime examples of metaphysical theories, and would even go this far as to claim that those theories (together with their contrary opponents) can be seen as definitional for the discipline of metaphysics.

The contingency of a theory can be expressed using possible world semantics. Let m be a metaphysical theory. Then we say m is contingent if there are (at least) two possible worlds w1, w2 such that truth values for m differ in w1, w2, and we say that m is necessary if m is not contingent.

The paper I read was situated in the post-Lewis metaphysic discourse that is sometimes simply identified with contemporary metaphysics. However from my previous reading of metaphysics outside this discourse, it would appear to me that no philosopher would endorse the claim that there is (at least) one metaphysical theory that is contingent. Rather, I took it to be a unanimously shared implicit opinion that all metaphysical theories express necessary truths.

What are reasons to think that there exists one contingent metaphysical theory? Especially, are there (good) reasons to think that prime examples of metaphysical theorizing express contingent truths? I'm looking forward to both doxographical answers and answers that contain good arguments.

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    If metaphysical theories express necessary truths, then how can there be alternative metaphysical theories? If there are not possible worlds in which materialism is true, and false, respectively, then how can materialism even be a theory? It would instead be a logical requirement of being a world, or it would simply be inconceivable.
    – user9166
    Jan 12, 2017 at 23:37

1 Answer 1


If we begin with the assumption that contingency and possibility are somehow based on the ontological nature of the universe, metaphysics could prove to be an impossible endeavor. We assert that there are necessary consequences because of a belief that all things are determined in some way by a certain orderliness which we refer to as laws, so it seem that such an idea of contingency would have to involve things happening without any such determination. If any given occurrence could take place in an undetermined manner, there would be no grounds to deny the possibility of any others being likewise undetermined, because the only grounds possible for such a denial would be an event's subjection to determination which is the very thing being questioned. On what basis could it be claimed that a lawless event is subject to any law? Even if some events are subject to law and others not, being a member of one class rather than the other would itself be a contingent fact. Consequently, all truth would be contingent and anything would seem to be possible. Therefore, using a Kantian sort of argument, we could say that the possibility of knowledge presupposes that contingency cannot have such a basis.

On the other hand, we speak of contingency and possibility all the time and they are indispensable concepts for conducting our affairs. This is due to the fact that we are greatly limited in our ability to discover the all the determinations of any given event. However, when we speak of contingency and possibility, it should be understood that this refers to the limits of our knowledge as opposed to some metaphysical fact about the universe.

This idea of possibility reflecting the limits of knowledge has been held by various philosophers. For example, Bertrand Russell said the following:

"Propositional functions, on the contrary, are of three kinds: those which are true for all values of the argument or arguments, those which are false for all values, and those which are true for some arguments and false for others. The first may be called necessary, the second impossible, the third possible. And these terms may be transferred to propositions when they are not known to be true on their own account. but what is known as to their truth or falsehood is deduced from knowledge of propositional functions. E.g. 'it is possible that the next man I meet will be called John Smith' is a deduction from the fact that the propositional function 'x is a man and is called John Smith' is possible—i.e. true for some values of x and false for others. Where, as in this instance, it is worthwhile to say that a proposition is possible, the fact rests upon our ignorance." (Bertrand Russell, The Analysis of Matter, p. 170, emphasis added)

Similarly, McTaggart asserts that speaking of possibility involves one of two things:

  • A statement about the limitations of our knowledge, or
  • An assertion that a given fact doesn't preclude another.

In the second case, he says that it's not really a question of possibility but about an actual state of affairs:

"We saw that 'it is possible that X should be Y,' if it was not a statement about the limitations of our knowledge, meant that the characteristic X does not imply the absence of the characteristic Y. It is thus a statement about the implication of characteristics, and is not, of course, a statement about their possible implication, but about their actual implication." (McTaggart, Reality and Existence, p. 36,37, emphasis added)

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