Reply To: Immediate Inference (Eduction)


Dear George W:

Thank you for that question. Clearly, SAP and SIP are not equivalent propositions. For one thing, one is universal and the other particular, and while the truth of SAP implies the truth of SIP, the truth of SIP doesn’t imply the truth of SAP.

When I say that eduction generates equivalent propositions, I’m talking about the three kinds I deal with, namely, (simple) conversion, contraposition and obversion. I confine my account to these three because other forms of eduction (e.g. conversion by limitation – from SAP to SIP to PIS) can be arrived at by means of a combination of the three kinds of eduction I mention and the inferences deducible from the square of opposition.

My account is a somewhat simplified treatment of the subject (but not falsified!) and it is so for pedagogical purposes. Just as one can get most of the information one needs for the operation of an electronic device from about 5-10% of a manual, so too, most of what one needs from the logic we’re dealing with here can be had from a slightly trimmed account. It may take a little longer to get where we need to go but the demands on memorisation and use are significantly less.

There isn’t, then, any conflict between my account and that of Joyce.

I hope this clarifies matters? If you have any remaining doubts, please do get in touch with me.

Best wishes,