Re: Is X a Y?

Nicholas Bostrom (
Mon, 28 Jul 1997 13:01:39 +0000

John K Clark <> wrote:

> >What about the old distinction in logical positivism between
> >propositions true (solely) in virtue of their meaning and
> >propositions whose truth also depend on how the world is?
> But that's the question, if something is logically consistent does that make
> it part of the world?

No, that is not the question. Not many would say that
consistency guarantees existence (apart from David Lewis). The
snowman is a logically consistent notion but that does not mean that
the snowman exists.

Now, obviously, if something is asserted to exist by a logically true
proposition, then it exists. So the questions are (1) Is the
proposition that the Mandelbrot exists logically true? (which boils
down to whether the notion of "logical truth" in the traditional
way really makes sense), and (2) Is this kind of existence somehow
fundamentally different from the existence of objects which cannot be
claimed to exist by any logically true proposition.

> I'm not a big fan of Logical positivism either,
> Russell's theory of types is really ugly.

You don't need to accept Russell's theory of types to be a fan of
Logical positivism.

>English is
> far from the best, and yet with all its imperfections people have still
> managed to get quite a bit of mileage out of it.


Now, I don't know whether I basically disagree with you or I am just
playing the devils advocate. But I do think that the question "Does
the Mandelbrot set exist?" needs to be specified and refined. I mean
there is the logical notion of existence, and then the answer is
obviously Yes. But you seem to have a thicker notion of existence in
mind, and until you have explained what that notion is, your question
appears rather meaningless to me. (I mean, if somebody told me "Yes,
the Mandelbrot set does exist.", how much wiser would I be if I
didn't know what this thicker notion of existence is supposed to be?)

Nicholas Bostrom

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