What kinds of things can exist? I have come up with six ontological categories:
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objects: rocks, airplanes, people, etc.
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events: wars, births, eating, etc.
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properties: color, position, temperature, etc.
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states: moving, living, running, falling, etc.
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abstractions: mathematics, love, time, etc.
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feels: pain, thought, emotion, etc.
First of all, I don’t mean to say that all these things exist as objective independent entities out there in spatiotemporal existence. What I mean to say is that these ‘ontological categories’ represent the different meanings we can attribute to the word ‘exist’. That is, to say that “X exists” determines the meaning of ‘exist’ only when it is determined what ontological category X belongs to. So for example, to say “cars exist” determines the meaning of ‘exist’ as “cars, as physical objects, occupy certain places out in the spatiotemporal world” but to say “mathematics exists” determines the meaning of ‘exist’ as “the subject we call mathematics is engaged in by human beings”. Or take the statement “pains exist” - this obviously means something to the effect that “pain is occasionally felt by sentient beings” - to exist in this case means to be felt.
It seems that, as divergent as these meanings for ‘exist’ are, we (perhaps surprisingly) typically have no trouble understanding the term’s proper use. It is never a question whether the statement “wars exist” is right or wrong. Everyone who isn’t insane or mentally defective in some way (or you’re not a philosopher ) knows that this statement is correct, that wars do exist. Yet it is equally never a question of what exactly ‘to exist’ means in this case. No one misinterprets the statement to mean that wars are physical objects sitting somewhere out there in physical space. We all know to interpret “wars exist” as “wars happen”. I don’t think there should be any reason not to carry this blatant common sense over into philosophy - the only prerequisite, I would suggest, is that we make clear (as it is one of philosophy’s primary functions to do) what this common sense understanding specifically says, and I offer the ontological categories above as one possible translation of what our common sense is telling us vis-a-vis the meaning of ‘exist’.
One question that has popped up for me is whether any one of the above ontological categories can be put in terms of any other. For example, we know that an event like war could be construed as a state - as in, the US and Iraq are in a state of war. Likewise, a state like war could be construed as an abstraction - war is, after all, intangible and immaterial (though it may involve tangible and material things - like guns, like soldiers, etc.). Also, I question whether certain properties (ex. red, temperature, solidity, etc.) can be put in terms of feels or mental states (ex. the sight of red, the feel of temperature and solidity, etc.). Physicalists, for yet another example, are in the habit of reducing almost everything (let alone mental states) to physical objects or systems. Even mathematics, with a real stretch, could be put in physical terms (whether that be the brain states of mathematicians when they do their work, or the symbols written in ink in mathematics text books, and so on). Besides these considerations, there is the consideration of whether certain categories depend on others. It seems to me, for example, that no property could exist unless it belonged to an object. The redness of my car, for example, could not exist without my car existing as a physical object. I might also consider whether properties could belong to abstractions (we do, after all, tend to talk about ‘abstract objects’) - for example, a war (as an abstraction) could be said to have the property of “being very bloody” or “being very long”. But I can’t imagine a property existing all by itself - that is, without something to have that property. Feels also come into question. Can a feel (ex. pain) exist without an object - that is, a body - to experience that pain? A theist, or dualist, might argue that it can. A soul that has left the body after death can go on to experience all manner of feels. Whether or not this is scientifically tenable (as many would argue it isn’t) is neither here nor there. The question is rather whether one can mean that a feel like pain or thought or emotion exists without having to presuppose some object (physical? abstract?) experiences that feel. A third consideration is whether certain categories ought to be classed together under one heading and distinguished only as sub-categories. For example, should the categories ‘objects’ and ‘abstractions’ be lumped together as ‘objects’ and under that category distinguish between (perhaps) ‘tangible objects’ and ‘abstract objects’. Or perhaps ‘material objects’, ‘immaterial objects’, and ‘abstract objects’ - that way, the theists would have a comfortable place to put God (i.e. as an immaterial object) for although they would all agree that God is not a material object, they would object to the notion that He is merely an abstraction. He certainly exists independently of our abstractions, they would say, but yet still in an immaterial way. On the other hand, Platonists might object to the bifurcation of ‘immaterial’ and ‘abstract’ since they tend to lump them together as the same sort of thing. Needless to say, there would be much to sort out if we went along with this idea of coming up with ontological categories.
Nevertheless, I think much in philosophy could be simplified if we could establish and agree upon a few basic ontological categories. It is often argued that because a thing is purely an abstraction (for example, time), it doesn’t exist. Whereas for others, this seems absurd - of course, time exists, they’d protest! Similar arguments over the existence of mental states have arisen. ‘Mind’ it is often argued, doesn’t exist - why? - because it is not an objective phenomenon subject to empirical observation (i.e. it is not a physical object). But again, this, from a different point of view, brings us into the absurd. If mind doesn’t exist, how is it possible for us to feel anything (for ‘feeling’ is quintessentially mental). I think the question of whether or not time, mental states, or any other entity whose existence is in question, exists is a misleading question. Rather, the question should be “which ontological category does it fall under?” Of course, what these ontological categories are is one of the questions I hope this thread will shed some light on (or whether the whole concept of ‘ontological categories’ is a bad idea). So I’d like for this to be one of the questions addressed in this thread. Others might be the questions I raised above - namely, about whether any ontological category can be restated in terms of any other, or whether any one depends on another, or whether any two (or more) ought to be lumped together and made into sub-categories. What would be the implications of this on the meanings we attribute to ‘exist’?