By Retroduction I mean that kind of reasoning by which, upon finding ourselves confronted by a state of things that, taken by itself, seems almost or quite incomprehensible, or extremely complicated if not very irregular, or at least surprising; we are led to suppose that perhaps there is, in fact, another definite state of things, because, though we do not perceive any unequivocal evidence of it, nor even of a part of it, (or independently of such evidence if it does exist,) we yet perceive that this supposed state of things would shed a light of reason upon that state of facts with which we are confronted, rendering it comprehensible, likely (if not certain,) or comparatively simple and natural.