RE: SUO: On the (existence of the) supreme supertype
Pat,
You state that causality should be prohibited from "unreal" to "real"
and vice versa. Although I can see that the unreal-to-real case should be
prohibited, I don't think the other direction should be strictly
insulated. For example, it might make sense to assert information about
"Adam's younger brother" (which doesn't exist) in an "unreal" world (or
context), but if there is no Adam in the real world there is an effect on
the unreal world which is that extra content (the existence of Adam) is
required to be in the unreal world.
This is a pretty esoteric quibble though and I agree with your main point.
Adam
At 10:36 AM 2/22/2001 -0600, pat hayes wrote:
>Phil, I won't say anything else about what we call T, but you do raise
>an important issue, which can be summarized as the question of whether
>existence should be a predicate. There is a potential mismatch between
>'exists' meaning actual existence in the real world and 'exists' used as a
>quantifier in the logic. If we want our logic to be able to reason about
>circumstances which might never actually obtain (as is often done in
>planning. by considering alternative possible futures, then deciding to
>perform actions which make some of them impossible; and as is also done in
>counterfactual reasoning), then we have to allow into the domain of
>quantification things which do not in fact exist in the first sense, and
>also be able to contemplate things which do exist having properties which
>they never in fact have. So just saying
>(exists (?x)(= ?x a))
>wouldnt be enough to assert that the thing called 'a' *really* exists; to
>do that one would need to say something more about this thing called 'a'.
>Exactly what more is an engineering question which we need to address.
>
>A common strategy is to introduce 'imaginary entities' or 'possibilia' as
>a distinct category in the classification heirarchy, but I would argue
>that this is a mistake, on several grounds. First, any kind of thing might
>be possible: one can have possible humans, possible events, possible
>worlds, etc.., so as a category this cuts across the entire classification
>spectrum. Second, it suggests that possible-but-unreal things are somehow
>another category of real things, much as birds are a kind of organism.
>This gives rise to many well-known concpetual puzzles and paradoxes, all
>arising from a basic misunderstanding. (Quine in a famous passage points
>out the error in going from 'it is possible that someone could have been
>standing in the empty doorway' to 'there is a possible person standing in
>the empty doorway', by asking *how many* possible but non-actual people
>every empty doorway has to contain?) And third, it masks the important
>point that these non-actual things almost always seem to be 'inside'
>non-actual worlds, ie we talk about an alternative set of circumstances or
>alternative possible worlds (in which, say, I had a brother who I don't in
>fact have), rather than putting the possible but non-actual things into
>this real world. And there is a good reason for this: if the
>possible-but-non-actual things were in fact actual, they would have real
>effects on the rest of the world. One cannot just insert a thing into the
>world and expect everything else to go on just as before; so one is forced
>into thinking about a wider set of circumstances than just the immediate
>surroundings of the imaginary thing. As we all know, one dead sparrow
>might have all kinds of repercussions, so it is usually safest to provide
>an alternative world for the sparrow to die in, and see what happens there.
>
>I think that a general-purpose SUO needs to allow non-actual entities - it
>cannot presume that the existential quantifier means existence in the real
>world - but that just allowing them casually, as it were, without some
>attention being given to their effects, is a well-known recipe for
>conceptual muddle. I would suggest that any nonreal thing needs to be
>thought of as enclosed within a non-real causal bubble which is large
>enough to provide a causal 'horizon' insulating any effects of the unreal
>thing from influencing any events in the real world, or vice versa. The
>safest such bubble would be an entire possible world, but we might allow
>somewhat smaller sets of circumstances or 4-d enclosing space-times to
>play the same role. Then the way to introduce 'possibilia' into the
>ontology is to introduce these 'bubbles', and allow 'IsReal' as a
>predicate on them (which asserts that that set of circumstances does in
>fact obtain in the real world somewhere/when). Then a
>possible-but-not-real person (eg my imaginary brother) is simply a normal
>person who has the misfortune to only be enclosed inside nonreal bubbles.
>This overall picture has no need for a special category of 'possibilia',
>therefore, and it is meaningless to even talk about possible-but-unreal
>things inside real worlds.
>
>Pat Hayes
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