The three kinds of reasoning may be designated by the letters A, B, C.
A is that process in which the mind goes over all the facts the case, absorbs them, digests them, sleeps over them, assimilates them, dreams of them, and finally is prompted to deliver them in a form, which, if it adds something to them, does so only because the addition serves to render intelligible what without it, is unintelligible. I have hitherto called this kind of reasonings which issues in explanatory hypotheses and the like, abduction, because I see reason to think that this is what Aristotle intended to denote by the corresponding Greek term ‘[apagoge]’ in the 25th chapter of the 2nd Book of his Analytics […] But since this, after all, is only conjectural, I have on reflexion decided to give this kind of reasoning the name of retroduction to imply that it turns back and leads from the consequent of an admitted consequence, to its antecedent. Observe, if you please, the difference of meaning between a consequent the thing led to, and a consequence, the general fact by virtue of which a given antecedent lead to a certain consequent.
