Carnap on what's 'really wrong with the Aufbau'

When I was going through some of the photocopied material I have from the Rudolf Carnap archive, I found the following interesting (to me) remark. Carnap is discussing with Nelson Goodman a draft of Goodman's dissertation (A Study of Qualities, which much later became The Structure of Appearance). Goodman points out various supposed technical defects with Carnap's method of quasi-analysis presented in the Aufbau, and Carnap says roughly the following:

The real problem with my Aufbau is not the various counter-examples that can be constructed against my particular version of quasi-analysis (which I already knew about), but rather the assumption of extensionality.

(I haven't quoted, because I don't think it's allowed.) I like this because (a) it's a really smart philosopher saying 'My book rests on a mistake,' and (b) it fits with my pet theory that the real break between Carnap and Quine stems in large part from Carnap moving away from the extensional languages he espoused in Logical Syntax, while Quine held fast to the extensional standard throughout his life (see the posthumous "Confessions of a Confirmed Extensionalist").


Shawn said...

That is pretty interesting. I do not know much about Carnap, so this question might be answered straightforwardly in his writing. Is there an indication about what motivated Carnap to reject the strict extensionality requirement that Quine cleaved to through his whole life? Was it the counterexamples to quasi-analysis he came across?

Greg Frost-Arnold said...

Hey Shawn -

I'm not 100% certain what, historically speaking, was the spark that initially drove Carnap away from the requirement of extensionality. But I do know that pretty soon after the switch, the reason Carnap was giving in print was that without allowing languages to be intensional, we cannot draw the difference between (to use Quine's favorite example) 'All renates are renates' and 'All renates are cordates.' (This is a bit of a toy example; the sentences Carnap was more interested in were those of physics.)