Wednesday, July 31, 2013

Is Existence a Predicate?

A friend of mine once referred to the statement that "existence is not a predicate" as Kant's Assertion.  I think that's an apt description, since there are really no arguments against existence being a predicate.  Yet, Kant's Assertion is often just repeated as if the matter is settled.  However, consider this argument:

1. Necessarily, if X and Y possess all of the same attributes, then X and Y are identical. (Premise, Leibniz's Law)

2. Necessarily, if some not-real A possesses all of the same attributes as some real B, then A and B are identical. (From 1)

3. A not-real A cannot possess all of the same attributes as B. (Premise)

4. Therefore, A and B are distinct. (From 2 and 3)

(1) states the relatively uncontroversial axiom of logic known as Leibniz's Law.  Now, if existence is not a predicate, then (2) requires that A and B possess all of the same attributes.  The problem is that A does not exist, whereas B does exist.  The only difference between the two would be existence, but since existence does not exist, it follows that A and B are distinct by nothing.  However, to be distinct by nothing is to be identical, which entails that A and B are actually identical and not distinct.  You can all decide for yourselves if that's a rational position.

If you're anything like me, though, you'll affirm (3) (and hence (4) as well) and reject Kant's Assertion.


  1. Doug, I think one problem is that (1) is not all that uncontroversial! The converse (indiscernibility of identicals) is not controversial. But the premise you stated (the identity of indiscernibles) is widely challenged, at least as long as you do not include among the properties under consideration "being identical to x" or things like that.

    Another thing is that people will object to you talking about 'not-real A's; since they are not existent then they can't be talked about or have attributes. I think this position is false, but many people will bring up objections like this I suspect.

    But I agree with you, I think existence is a real predicate and Kant's Mere Slogan has little backing. Will be doing my honor's thesis on this topic in the fall. If you want I can share with you some of the arguments I have been thinking about.

  2. This argument seems to beg the question. Premise 2 entails that the only diffrence between a non-existing thing and an existing thing is a predicate called existence, which is in fact what you are trying to prove.
    In reality the difference between a non-existing white horse and an existing white horse is not some predicate called existence, but predicates like 'horseness' and 'whiteness', which the non-existing horse lacks. A non-existing white horse isn't white since non-exsitingg things have no attributes.
    I am not saying Kant is correct, BTW, but your argument in no way proves that he isn't.

  3. Alfredo, I suppose I just see (1) as obviously true, even though it has some detractors. It just seems weird to me that anyone would object that we cannot talk about a not-real A, as if imaginability is just thrown out the window. Nevertheless, I agree with you that people will make that objection. Keep me up to date every once in awhile with respect to your honor's thesis. I know you'll knock it out of the park!

  4. Walter, it's actually premise (3) that implies existence must be a predicate. (2) isn't even a premise, but rather a logical inference from (1).

    When you say non-existing things don't have attributes, are you saying that all attributes must have instantiation? That would indeed call into question (2), as well.

    1. I am saying that I don't think not-real things "possess" anything. I guess this also entails that all attributes must have instantiations,otherwise they would not be attributes. So, yes, i am calling into question premise 2, and so are lots of other people, including philosophers. Which does not mean I am right. the nature of existence is a very difficult matter and I don't think your argument dissolves it.

    2. Oh, I wouldn't make such a bold claim as to say that my argument "dissolves" the matter. Virtually no argument in philosophy is universally agreed upon. I don't consider the argument a proof, but rather as a reasonable argument that many who proudly boast of Kant's Assertion ought to take note of. I just find it counter-intuitive that all attributes must be instantiated. I'm not saying it's unreasonable, but it seems a lot weirder to me than claiming that existence is a predicate.

    3. But in the end, what it comes down to is what you are I find weird or not, but I don't see, "I find your position weird" as an argument.
      I think Kant made uttered his 'Mere Slogan' (as Alfredo puts it) because existence as a predicate would lead to very weird notions.

  5. I didn't say that the weirdness of a proposition makes it untrue or unlikely. I find String Theory *really* weird, but for all I know, it's true.

    Kant rejected the notion that existence is a predicate in part because he rejected the classical arguments for God's existence (though he accepted a pragmatic moral argument in his Critique of Practical Reason), even suggesting that the cosmological argument is dependent on the ontological argument. He classified the noumena (what a thing really is in and of itself) as unknowable, leaving only phenomena (what is perceived) as knowable. If one accepts such a view, it doesn't take much to get to the conclusion that existence is not a predicate, since even if existence were a predicate, it would be part of the noumenal realm.

  6. In fact, in the Critique of Pure Reason, Kant remarks that there is intuitive support for the notion that existence is a predicate, giving the example of a person preferring an existing fortune as opposed to an imaginary one. He didn't reject this view because he thought it was weird, but because it conflicted with some of his metaphysical commitments.