Dual Aspects of Abduction and Induction

A new characterization of abduction and induction is proposed, which is based on the idea that the various aspects of the two kinds of inference rest on the essential features of increment of (so to speak, extensionalized) comprehension and, respectively, of extension of the terms involved. These two essential features are in a reciprocal relation of duality, whence the highlighting of the dual aspects of abduction and induction. Remarkably, the increment of comprehension and of extension are dual ways to realize, in the limit, a `deductivization' of abduction and induction in a similar way as the Closed World Assumption does in the case of the latter.