Wednesday, February 18, 2009


Some expression are rigid in the sense that they have a constant (secondary) intension, while others are nonrigid. And some expressions are stable, in the sense that they have a constant character, while others are unstable. Moreover, some expressions have combinations of the rigidity and stability properties. 

Constants (e.g. logically proper names?) are both rigid and stable. Indexicals (e.g. `I', `tall') are rigid but unstable. Vacillators (e.g. `kangaroo', `the inventor of bifocals') are stable but nonrigid. 

Are there any expressions that are both unstable and nonrigid?


Lars said...

What about (complex) expressions like "my favourite aunt", "your first pet", etc.?

Brian Rabern said...

yeah, those do fit. but they are "impure" mixes of definite descriptions with indexicals in them. many sentences would also work.

i guess i was looking for a pure case where an expression E varies its content with context and also given a fixed content varies its extension with circumstance.

maybe limit it to only simple expressions. assuming there are simple expressions that are nonrigid. and i guess there are: many general terms and predicates should actually be in the nonrigid camp.

cathalcom said...

what about 'thing' ?