TheExistenceOfPhysicalObjects|Talk

In the main article I was trying to explain some of the main traditional lines of argument about this topic. To my knowledge, which might possibly be inadequate, what is below really is not part of that tradition (unless you'd want to rewrite it to make it reflect Berkleyan idealism). Let me reply to some of it (since I'm very interested in this topic these days, it so happens, on a professional level--i.e., I have a Ph.D. in philosophy and I have been reading journal articles on the subject, and writing and thinking about it to myself).

:A further argument for the definability of existence is a corollary and extension of the PhilosophyOfPerception.

The philosophy of perception is a subject matter, and consequently doesn't by itself have any corollaries (as though it were a theorem or an axiom).

:That is, if it can be perceived with the physical senses, then it exists.

Is this esse is percipi all over again--see George Berkeley.

: Well, what makes a thing perceptible? The quality or property which makes a thing perceptible is that it is capable of affecting and of being affected. This is how one perceives; one either creates an effect and receives the sensory feedback of having done so, or one witnesses the result of an effect created. When light reflects from a big, red apple, it is because the apple was capable affecting the light so as to alter its direction and absorb certain wavelengths while reflecting others. Consequently, the eye is able to detect the altered light and identify its new properties.

:Hence, otherwise invisible energies and particles can be confirmed to exist by the effects they suffer or create. Magnetism, gravity, ultraviolet light, cosmic rays, all are included within the realm of existing things.

Here you are addressing a different problem from the one raised in the article; the name of your topic now is scientific realism, and that is the question whether the unusual theoretical ("unobservable" for example) entities posited by science are real, and what it might mean to say that they are real or exist. The question at issue in TheExistenceOfPhysicalObjects is "simpler" or more fundamental: what does it mean to say that anything exists at all? What does it mean to say that the eye, sensory feedback, and other physical objects exist? Perhaps, many philosophers say, existence isn't a property at all; in which case we shouldn't expect to be able to give a definition of 'exists', at least not a "first-level" definition (this isn't something I mentioned in the article...I could have done a better job with it, but I was writing for undergraduates who had never thought about this stuff before).

: Taken further; since awareness, emotions, imagination, dreams, etc. are likewise capable of affecting and being affected, they could be said to exist.

So:

X exists if, and only if, X is capable of affecting and being affected.

So how do we decide that something exists? Why, we ask whether it is capable of affecting and being affected. Well, how do we determine whether something is capable of affecting and being affected?

: One might say "I feel sadness." It could hardly be argued that sadness does not exist and so the person, contrary to his assertion, could not possibly feel sadness. Clearly, he does. The nature of the existence these intangibles is qualified and quantified by the nature of the effects they create and receive. Thus, unicorns could be said to enjoy a form of existence. They exhibit an imaginary existence. One imagines them, conveys the substance of this imagined existence to others, and thereby affects the imaginations of others to replicate said existence in their own imaginations. When a child learns from adults that there are no physically existing unicorns, his imaginary unicorns may lose their appeal or suffer destruction. This imposition of effect by physical existence on imaginary existence can also work in the reverse. An artist may "imagine" a finished canvas. Absent this precursor, imaginary existence, the physical canvas might never exist.

It seems to me you've refuted yourself. We're looking for a definition of the existence of physical objects. If, according to your definition, unicorns exist, since they don't in fact exist, your definition is wrong. Now, you can play semantic games and say that they enjoy "imaginary existence"; you can say whatever you want, but what difference does it make?

I borrow from Hume:

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All reasonings concerning matter of fact seem to be founded on the relation of Cause and Effect.

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The hearing of an articulate voice and rational discourse in the dark assures us of the presence of some person: Why? because these are the effects of the human make and fabric, and closely connected with it. If we anatomize all the other reasonings of this nature, we shall find that they are founded on the relation of cause and effect, and that this relation is either near or remote, direct or collateral.

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When it is asked, What is the nature of all our reasonings concerning matter of fact? the proper answer seems to be, that they are founded on the relation of cause and effect.

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It may, therefore, be a subject worthy of curiosity, to enquire what is the nature of that evidence which assures us of any real existence and matter of fact, beyond the present testimony of our senses, or the records of our memory.

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Sight or feeling conveys an idea of the actual motion of bodies; but as to that wonderful force or power, which would carry on a moving body for ever in a continued change of place, and which bodies never lose but by communicating it to others; of this we cannot form the most distant conception. But notwithstanding this ignorance of natural powers and principles, we always presume, when we see like sensible qualities, that they have like secret powers, and expect that effects, similar to those which we have experienced, will follow from them.

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Now whatever is intelligible, and can be distinctly conceived, implies no contradiction, and can never be proved false by any demonstrative argument or abstract reasoning a priori.

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We have said that all arguments concerning existence are founded on the relation of cause and effect; that our knowledge of that relation is derived entirely from experience;

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The existence, therefore, of any being can only be proved by arguments from its cause or its effect

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I am afraid I, like Hume, blurred the line somehat between physical objects and less tangible things, but he tended (as one might expect from his time) to speak in rather concrete terms and to dwell in specific physical reality (while seeming to hold that thoughts, though ephemeral, were real and existed in no different wise than physical objects). Perhaps I would have done better not to stray into the realm of thought. However, his argument for the definability of existence (including the existence of physical objects) is not location in space, but Cause and Effect. And I happen to like his argument better. It was this argument I thought to exposit in more modern terms, to add to the arguments for the definability of the existence of physical objects.