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Re: Extensional modals?

Hi Avi, thanks for the clarification and advice. I have another query: in chapter 11 section 5 on Temporal Modality you write about how sometimes permutation can result in wrong inferences, and give two examples.

1. S is M, M are always-P, therefore S is always-P
2. S is M, M are sometimes-P, therefore S is sometimes-P

Maybe I'm getting ahead of myself here, because in a later paragraph you write "All this will become clearer by and by", but aren't the above syllogisms valid?

Re: Extensional modals?

Hi McCoy. No, that is the point, these syllogisms are not valid, as you will see when you get to syllogism. The modality cannot be attached to the predicate - it is a modification of the copula (i.e. the relation between the subject and predicate).
Avi - P.S. sorry my previous post was difficult to read, I was very busy with other things at the time.

Re: Extensional modals?

Avi Sion
Hi McCoy. No, that is the point, these syllogisms are not valid, as you will see when you get to syllogism. The modality cannot be attached to the predicate - it is a modification of the copula (i.e. the relation between the subject and predicate).


Right. I'm getting ahead of myself again.

P.S. sorry my previous post was difficult to read, I was very busy with other things at the time.


No problem, I understood what you said.

Re: Extensional modals?

Feel free to ask questions when in doubt.

Note that the first syllogism you quote, viz. 1. S is M, M are always-P, therefore S is always-P, has a lesser valid conclusion, viz. S is P (without the always).

Whereas the second one, viz. 2. S is M, M are sometimes-P, therefore S is sometimes-P, does not have any valid conclusion.