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Re: Is logic "purely" formal?

Hi Avi, thanks. I had a feeling there was something fishy about it, but couldn't put my finger on where the error was.

Avi Sion
Hi Smith.
Furthermore, the contraposite there presented is misleading. The real contraposite of “If Baby cries then we beat him” is not “If we do not beat Baby then he does not cry,” but “If we did not beat Baby it can be assumed that he did not cry,” i.e. “if we did not beat him it is because he did not cry.”

Right. In this case the 'if then' is being used in the sense of causality, so the proposition could be expressed as 'baby crying causes us to beat him' in which case the contrapositive would be 'not beating baby "causes" him to not cry'. It doesn't mean that he may not be crying for other reasons, only insofar as 'we are not beating him'.

To be fair to Stove, I don't think he was attacking logic, at least, I assume he wasn't if he's written a book called 'The Rationality of Induction' (although I haven't read it). But then I wonder what his point is. It seems trivial to say that there are restrictions on the value a variable can take, but that doesn't make logic any less formal, any more than the need to restrict values in some mathematical formula makes maths 'informal'.

Anyway, I'm happy to have found your site.

Re: Is logic "purely" formal?

Hi Smith, thanks.

I haven't read Stove's'The Rationality of Induction', so I do not know what he advocates in it. I ought to read it, but I have a pile of books I still want to read waiting for me.

If you're interested in Induction, I strongly recommend my book 'Hume's Problems with Induction', which should inoculate anyone against fallacious claims regarding this subject.

You can read it online here: Or you can buy it at or at in softcover or e-book form.

If you leave your e-mail address at, I will add you on to my mailing list for future announcements.

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