Logic and Reasoning: do the facts matter?

1 Drawing borders Logic arose in Antiquity from two sources: the study of real argumentation in the dialectical tradition, and that of axiom-based proof patterns organizing scientific inquiry. Over the centuries that followed, the discipline turned abstract and eventually, profoundly mathematical. Is logic still about human reasoning? Or is it, as Kant and Bolzano said, about an abstraction in the realm of pure ideas? In the latter vein, logical consequence is an eternal relationship between propositions, firmly cleansed from any mud or blood stains, smells, or sounds that human inferences might have – and therefore also of their colours, and tantalizing twists and kinks. Put in another way, do the empirical facts about human reasoning matter to logic, or should we just study relationships between proof patterns, and the armies of them that we call formal systems, in some eternal realm where the sun of Pure Reason never sets? Most logicians think the latter – and accordingly, the precise relation to reasoning practice is left open. Universities should just hire logicians for their intrinsic cultural value, and no questions asked: in Tennyson’s immortal words, “theirs not to reason why”. Of course, if pressed, many logicians and philosophers would say that logic is normative; it describes correct reasoning. People would be wise to follow its recommendations – but so much the worse for them, if they do not. In fact, did not Wilkie Collins, one of the first mystery writers 1 say it all, in the immortal words of the family butler Gabriel Betteredge (The Moonstone, 1868):