Thursday, November 23, 2006


Yesterday's LOGOS-seminar saw Manolo M. give a talk on conceivability (indeed, on ideal conceivability, but I don't want to focus on that here). As Roman pointed out, conceivability is a somewhat loose term. However, it seems that most LOGOS-members share a very similar conception of conceivability, differing only in the details (I also encountered signs of this fact in the RG on Fictionalism).

My question is simply, what is that common conception? (...) It is part of another project that this blog can be used for, that is making the common ground of the group explicit such that new members, like me, can position themselves relative to it (I take the essentialism-discussions earlier to be part of that project).

Maybe you don't think that you in fact share any view on conceivability in the group. To illustrate, let me briefly tell you what I think of conceivability, and I think most of you (except for the other newcomers) will have similar objections to make.

I can make sense of three ways to explicate conceivability:
1) The first is very close to imaginability, and in that sense an object that is green and red all over is inconceivable, but so is an object displaying a billion different colours, because that's just too much for my imagination.
2) The second includes, but is not exhausted by, anything that can be expressed by a sentence I can understand. In this sense, it's perfectly conceivable that 1=0.
3) And then there is conceivability relative to a set of ex- or implicitly stated assumptions. In that sense a proof for the continuum hypothesis from ZFC is inconceivable; it's also (in most contexts) inconceivable that Spain will invade Iran over the next few months.

So, straighten me out!


Oscar Cabaco said...

I disagree with respect these 3 elucidations of the notion of conceivability. We may sometimes use the notion of “conceivable” meaning something along the lines of (1) or (3) (and mostly in non-philosophical contexts), but we never mean something like (2). Besides, I think you missed the use of conceivable most relevant for our discussions in philosophy. According to this sense of the world, “conceivable” is just the analogue for the epistemic modality of the word “possible” for the metaphysic modality. Therefore, conceivable can be defined this way:

It’s conceivable that P = It’s not a priori that not-P = It’s not ruled out a priori that P
It’s unconceivable that P = It’s a priori that not-P = P is ruled out a priori.

Of course this can be only half of the story. Now I must tell what “a priori” means. An standard definition (found in the Internet Encyclopedia of Philosophy) is:

A proposition is knowable a priori if it is knowable independently of experience. A proposition is knowable a posteriori if it is knowable on the basis of experience.

(See this for more details.)

Of course there are some important details that must be clarified in this definition, and there are several ways in which this initial characterization can be developed, but this is the standard (and historical) point of departure for any account of the notion of apriority.

Anyway, the relevant point is that according to this sentences like “There is an object displaying a billion different colours” and “Spain will invade Iran over the next few months” turn out to be conceivable. Likewise, the sentence “1=0” turns to be perfectly unconceivable.

Andi said...

Thanks, that was exactly what I was looking for. Does everyone agree with Oscar that this is the way to define conceivability? (Comments by nonLOGOS people highly welcome as well, by the way!)

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