Sunday, January 09, 2011

A problem for the Brentano thesis

As discussed yesterday, a 'Brentano equivalence' holds when we can convert existential sentences of the form 'an A-B exists' and categorical sentences of the form 'Some A is B'. The Brentano thesis is that every such (genuinely) categorical sentence is convertible.

This effectively amounts to the claim that any sentence of the form 'something is such and such' is existential. If anything is such and such, then that thing is an existing thing. The range of our natural language quantifiers 'every' and 'some' covers the entire realm of existence. Every thing is an existing thing.

There are strong arguments for this thesis. But there are strong arguments against, as well, which brings us back to the problem of intentionality. Surely the following inferences are all valid.

  • Jake is looking for a gold mine in Surrey, therefore Jake is looking for something (namely a gold mine in Surrey).
  • Bill wants a cigarette, therefore Bill wants something (a cigarette).
  • Andy is thinking about Pegasus, therefore Andy is thinking about something (Pegasus).

The problem is that any of these antecedents could conceivably be true, the inference seems valid, yet the 'something' in the consequent does not appear to be any existing thing. Clearly Jake can be deludedly looking for a Surrey gold mine, and so looking for a mine, and so looking for something. Yet, as far as we know, there are no gold mines in Surrey. The simple categorical sentence 'Jake is looking for something' can be true, without requiring that the something exists, contra Brentano.


David Brightly said...

>> 'Jake is looking for something' can be true, without requiring that the something exists, contra Brentano.

Perhaps I'm being fastidious, but is it contra Brentano? To get via Brentano to an existence assertion of the form 'an A-B exists' we first need to get to 'some A is B'. But we can't get from 'Bill wants a cigarette' to 'some cigarette is wanted by Bill'. Maybe the only cigarettes are Gauloises and Bill hates Gauloises.

It seems to me that the 'intentional object', the something in all these cases is less of a description and more of a specification:

Jake is looking for an entity that meets the spec (a) is a gold mine and (b) is in Surrey. Bill's want will be satisfied by an entity that (a) is a cigarette and (b) is not a Gauloise. Andy is thinking about an entity that meets the spec (a) is horse, (b) has wings.

In a nutshell: something != some thing.

David Brightly said...

Thinking about the cigarette example has suggested another aspect of intentional contexts. Suppose Fs are Gs. From 'Bill bought an F' we infer 'Bill bought a G'. We can generalise within the context. But from 'Bill wants an F' can we infer 'Bill wants a G'? I'm not so sure. If Bill were given a G that wasn't also an F his want might well not be satisfied. His specification isn't being met. I think this accounts for the nagging worry I had reading BV's interpolation on Peter Lupu's post. He says ' You can't want a motorcycle without wanting a heavy metallic spatiotemporal particular'. Hmm. I don't want no stinkin' heavy metallic spatiotemporal particular, I want a Harley!

Edward Ockham said...

Correct. However, the problem is that in both modern and traditional logic the particular proposition is convertible. I.e. in traditional logic ‘some A is a B’ (e.g. some man is an animal) converts to ‘some B is an A’ (some animal is a man’). This is even more obvious in modern logic: ‘Ex man(x) and animal(x)’ is equivalent to ‘Ex animal (x) and man(x)’.

It’s obvious for the reasons you state that something odd is going on, and it’s not a problem for the Brentano equivalence, but rather for the convertibility of simple propositions. I had planned to deal with this in a later post.