Re: Is It True What They Say About Tarski?

Daniel Fabulich (
Fri, 22 May 1998 23:23:51 -0400 (EDT)

On Fri, 22 May 1998, Christian Whitaker wrote:

> I suppose one could solve the vagueness of blue by assigning it a strict
> definition. Blue is light with a wavelength of 550 nm. Given such a
> definition, the truth value of the statement 'le ciel est bleu' must be
> no, as the value will be something other than precisely 550 nm, and will
> fluctuate across the horizon and from second to second as light is
> marginally refracted by water vapor and other chemicals inthe
> atmosphere. The only way to get a true Trotskian statement on sky color
> is to limit sky to a particular point in the sky to a particular point
> in time and find the precise wavelength. In practice this will not be
> very useful, because nobody says things like, 'le ciel est bleu at a
> point 67 degrees and 35 minutes above and 23 degrees and 12 minutes to
> the left of my reference point at exactly 3:57 PM.', even in a
> metalanguage.

On the contrary: rather, nobody uses metalanguages in day to day
conversation. (Lojban advocates, this is where you can pipe up if you
feel like it. :) ) If we did, however, you're right, this is the sort of
thing we'd say.

> I like Bart Kosko's notion that Trotskian statements should be
> assigned a fuzzy truth value.

NO, and this is where me must take care. First, I presume you mean
TARSKIAN statements. ;) Second, we may say that our INFORMATION is
imprecise, but the TRUTH is not. When properly defined, the sky is or is
not blue; we may be only 99% certain of its blueness on a clear day at
noon, but that is VERY different from saying that the sky is 99% blue
(again, restricted by our formal metalanguage).

We already quite often say in science that the wavelength of certain light
is 550 +/- 10 nm. This is not to say that the wavelength varies, but
that our information is imprecise. So, to the extent that it is
necessary, when we need to make clear how certain we are of something, we
will add the precision to which we think we know it.

We don't need "fuzzy truth" statements: the truth is binary, and we
already have a means of communicating precision.