The existence of physical objects

Suppose that 'exists' does have different senses, so that, if it could be defined (analyzed, explicated), one might define it for physical objects, for properties, for relations, for facts, for possibilia, etc.

In that case, what does it mean to say that a physical object exists? One might try to fill in the blank in the following: "An object exists, if and only if, it ... ."

A common view is that this question cannot be answered. It has been suggested that "exists" simply cannot be defined. That people very well understand what it means to say that an object exists is not necessarily to say one can define it. This is a very influential view, which many very smart people hold. But the initial assumption will be made here that we can define "exists" for physical objects.

Here is a starting point for this assumption. What is existence constrasted with? There are different kinds of nonexistence. So it has been proposed that the existence of physical objects is an "excluder" concept, as it were a purely negative concept: an item is actually in the world, it is not fictional; it is real, not imaginary; it is an actual phenomenon, it is not part of a false hypothesis; and it is located at the present time, not just at a past, or a future time.

Common sense would seem to have it, however, that there is one basic sense in which physical objects actually do exist, and that is as an object that belongs to the space-time system that is the world with which people are in direct contact. If one can bump into it, it exists. So one might boldly give this following definition:

Physical object O exists if, and only if, O is, at present, spatially located in the universe with which we are in contact.

This definition would seem to express a common sense notion of existence. Interestingly enough, though, only a few philosophers have given such definitions. [Bruce Aune], for example, in an introductory philosophy textbook, gives a definition much like this one.

This sort of definition encounters some serious objections. Consider the following objection, probably the most widespread.

There are many philosophers today, following Hume, Kant, Frege, and Russell, who claim that existence is not a property, or that 'exists' is not a predicate. Typically, the discussions in which this claim arises are discussions of the existence of physical objects. So, for example, the Eiffel Tower exists. This is a true claim; what makes it true? One would like to be able to say that it is the fact that the Eiffel Tower has the property of existence. It seems that the claim asserts that existence is a property of the Eiffel Tower. Yet the philosophers listed--with qualifications we perhaps need not go into right now--deny that existence is a property. In fact, this is the common view among philosophers today.

One might wonder why it matters at all whether or not existence is a property. Consider: if existence is not a property, then the concept of existence cannot be defined, or at least, not as it has been defined here. The foregoing definition of 'exists' is incorrect just because the definition does treat existence as a property.

Kant wrote:

By whatever and by however many predicates we may think a thing--even if we completely determine it--we do not make the least addition to the thing when we further declare that this thing is. Otherwise, it would not be exactly the same thing that exists, but something more than we had thought in the concept; and we could not, therefore, say that the exact object of my concept exists. If we think in a thing every feature of reality except one, the missing reality is not added by my saying that this defective thing exists. On the contrary, it exists with the same defect with which I have thought it, since otherwise what exists would be something different from what I thought. (Critique of Pure Reason, B627-8)

Suppose one listed out all the properties and relations of an apple sitting on a table. It is red, it has a stem, it is four inches wide, it is juicy, it is on the table, it is in a room, and so on. CONTINUE WIKIFICATION FROM HERE Kant says, then, once one has listed out all the properties and relations of the apple, one could try saying that the apple exists. But that wouldn't add any new property to the thing, Kant says. Therefore, existence is not another property over and above all these. So in other words, Kant argues as follows: a complete list of an apple?s properties would not be expanded by adding another property, namely existence; therefore, existence isn't another property over and above all the other properties.

So -- does that mean that existence is not a property at all? Well, no. If one lists out all the properties of the apple, the list would include "being located in the universe with which we are in contact." That particular property just is what makes the apple exist. That property would, of course, be included in a list of all of the apple's properties; so then consider this claim of Kant's, that existence isn't another property over and above all its other properties. Well, that's right, it's not another property. But that by itself doesn't mean that existence isn't a property at all! So Kant's argument just doesn?t appear to prove its alleged conclusion.

Consider also how [John Hospers] interprets Kant's argument. Maybe Hospers can make Kant look better. To quote Hospers:

"If we say that a horse has a mane, a tail, four legs, and hoofs, we are attributing properties to the horse; but if we go on to say that the horse exists, we are not adding another property: we are saying that the thing we conceived as having these properties also exists. We are not adding to our concept of the thing: we are asserting a relation between the concept and the world."

Hospers says here that when we say that a horse exists, we aren't attributing a property to the horse; we are "asserting a relation between the concept," the concept of the horse, "and the world." That's what he says; but on further reflection, one can see that it's not quite right. To say the horse exists isn't to assert something about the relation between the concept of the horse and the world; it is to assert something about the relation between, well, the horse and the world! Namely, that the horse is in the world! And one can have a concept of a particular horse that exists, and that concept would have that horse located in the observable world; and one can also have a concept of a particular horse that doesn't exist, and that concept would have that horse not being located in the observable world. So again, Hospers' argument apparently isn't valid. It just doesn't prove that existence isn't a property. All that it proves -- and it does prove this -- is that existence isn't a different property from the other properties of a thing.

But the dialectic definitely doesn't end there. Much more can be said on both sides. To really get to the heart of why so many philosophers these days think that existence can't be defined, one would have to explore much more logic. Present time and space do not permit this.

/Talk