Why isn't existence a predicate?

Question

According to SEP

There are two sets of reasons for denying that existence is a property of individuals. The first is Hume and Kant's puzzlement over what existence would add to an object. What is the difference between a red apple and a red existing apple? To be red (or even to be an apple) it must already exist, as only existing things instantiate properties.

Contra this, one can try out the sentences 'White unicorn' and a 'white existing unicorn'.

Here the adjective, or qualifier 'existing' actually adds something to the sense of the sentence; after all, for those who know that unicorns don't exist, to be told that they are adds something to their knowledge of the world.

To put the second sentence into subject-predicate form; one should say 'A white unicorn exists'...

(To which, the correct response, considering that I am a reliable informant, should run along the lines like 'My God - unicorns! really...where? Did you get some video footage...')

Notably the first sentence 'white unicorn' is just a sentence fragment, or a description; which might indicate some connection with Russell's theory of descriptions.

Why then isn't existence a predicate?

Answer 1

I think the issue mostly arises from having an insufficiently rich language to describe just-the-actual-world vs. model-worlds. When you can't cleanly distinguish between the two, existence becomes problematic. If there is no red apple, simply saying "a red apple" is already a problem since it does not refer to anything.

One solution is to use modal logic. One can define a non-problematic (or at least less-problematic) type of existence like so:

E(t) := ∃x(x=t)

But one needn't necessarily go to such lengths: just say that existence is a property of your model objects (regarding how they correspond with reality) and don't make such a claim about actual objects, and you're pretty much free of problems.

Answer 2

You say "one can try out the sentences 'White unicorn' and a 'white existing unicorn'. Here the adjective, or qualifier 'existing' actually adds something to the sense of the sentence; after all, for those who know that unicorns don't exist, to be told that they are adds something to their knowledge of the world. "

But the expression 'white existing unicorn' is not a sentence, but rather a noun phrase. As soon as you make it into a sentence, you get existence in either case.

(A) some unicorn is white

(B) some existing unicorn is white.

The first asserts that some, i.e. at least one, unicorn is white. The second asserts the same thing, but adds the redundant information that the unicorn is existing.

If you object that (A) could be true because it says in some story that a unicorn is white, I reply that in this sense (A) is elliptical for "according to some story, some unicorn is white". This does not assert the existence of unicorns.

Answer 3

Grammatically, of course, 'exists' is a predicate. 'The Lincoln Memorial exists' involves a predicative use of 'exists'. Whether existence is a property is another matter. And it's because it is widely assumed that existence is not a property, hence the predicate 'exists' has no property corresponding to it, that 'exists' is (while grammatically a predicate) not a 'real' predicate.

The thinking behind this is as follows.

If I say :

X is blue

X is square

X is heavy

it seems not unreasonable to assume that everything that is blue, square, and heavy exists. Hence X exists : how could X have these properties, how could these predicates apply to it, if it did not exist ?

So if I make a second list :

X is blue

X is square

X is heavy

X exists

what have I added ? It is not possible for the first three statements to be true and the fourth ('X exists') false. 'X exists' has added no information. But if existence were a property, it would add extra information. Therefore existence is not a property; and the predicate, 'exists', corresponding to it, is in this sense not a real predicate.

This explains, I think, why 'exists' is standardly taken not to be a predicate. And there plainly is something wrong in saying 'X is blue, square, and heavy - and also exists'. However, when one says 'it seems not unreasonable to assume that everything that is blue, square, and heavy exists', this seems precisely to concede that existence is a property. If it is a property, why shouldn't 'exists' be a perfectly proper, not at all 'unreal', predicate corresponding to it ?

Meinong can, of course, be brought into play but to extend the answer to include Meinong would take us too far into dense and complex territory. Meinong's views need a separate question.

REFERENCES

Kant, Critique of Pure Reason, A598/B626-A600/B628.

C. Heathwood, 'The relevance of Kant's objection to Anselm's ontological argument', Religious Studies, Vol. 47, No. 3 (SEPTEMBER 2011), pp. 345-357.

Answer 4

Not so much an answer as an annex to @GeoffreyThomas.

The question exposes some considerations to keep in mind when using "exist(ance)" in a formal context. To illuminate this it is helpful to use the ontology of Alexius Meinong:

https://plato.stanford.edu/entries/meinong/#ObjTheOntBeyBeiNonBei

and specifically his types of objects:

https://en.wikipedia.org/wiki/Alexius_Meinong#Types_of_objects

We can restate the three types as follows:

1) Things that can be named. 2) Things that may be conceived. 3) Things we can literally point out to each other.

Considering something like a square circle we see that it can only satisfy the first type. In this case we could never use a quantifier in relation to the object. "Exist" could only be used as a property and then also only as a negated one.

The table in front of me is clearly within the description of all three types. Here it would be appropriate to use a quantifier such as "exist", but also "exist" is a special kind of property, one that lifts the object out of the realm of contemplation into the physical and sensible. Note Meinong attributes "temporal" too

It is objects that satisfy only the first two types that are a little more tricky. For instance mathematical objects, does a number exist? In some philosophies numbers aren't real, thus the property "exist" would not exist. But then again there may be systems where some concepts are "real" and some concepts not. In this case, "exist" as a property would be applicable on a per concept basis. The actual formal system in use is a deciding factor on how "existence" can be applied, but the ontology can limit the availability of properties.

Answer 5

I think the problem arises from the assumptions inherent in the philosophical subject-predicate form.

The underlying principle seems to be that the predicate should qualify the subject in the sense that it becomes more specific; it should refine it. So

"A ball is in my garden" is refined by "The ball in my garden is blue".

The problem with existence as a qualifier is that it trumps the subject - we cannot say anything meaningful about the subject before we know whether or not it exists. And

X does not exist

could be said of a great number of different kinds of X without altering the reality being described (this is the sense in which I say it trumps, or is more important than the subject). Non-existence is indiscriminate - whatever it is that is said to not exist, the statement still amounts to the same thing - an absence of anything.

I can only suppose that this is the reason that the assumption of the Subject-Predicate construction in Philosophy seems to be that the subject exists. If existence of the subject X is assumed, X exists is redundant and X does not exist is paradoxical.

However natural language does not make this assumption and so sentences such as "Dragons do not exist" and "There is a solution to this problem" have semantic value.

So, to put it another way, Kant is simply pointing out the assumption in the Subject-Predicate construction.

Answer 6

I agree with Rex Kerr that "the issue mostly arises from having an insufficiently rich language". However, Kant went to lengths to resolve the issue by distinguishing the 'real' from the actual.

For Kant, the 'real' is the possible, and the actual is the real that has been observed; Existence is made in the interaction of observer and the observed.

So there are two major redefinitions from everyday language here: the real and existence.

To appreciate these redefinitions one has to approach things phenomenologically: one's experiential point of view is the start point. Then you can introduce the real. For example, walking down the street, there is a real possibility that there is a car around the corner. In negotiating the world this possibility is treated as a real thing; the world is full of such possibilities, their sum constitutes 'reality', (in Kantian terminology).

In contrast, actuality is that part of the world that has been observed, confirmed or created.

Turning the corner to discover the car does not add to the concept of the car; the car has not been changed by being observed. Hence, existence is not a predicate.