A general who during a battle must instantly risk the existence of a nation either upon the truth of a certain hypothesis or else upon its falsity, must perforce go upon his judgment at the moment; and his doing so is in so far logical that all reasoning is based upon a tacit assumption that Nature, in the sense of the aggregate of truth, is conformed, more or less, to something similar to the reasoner’s Reason. This kind of inference may be called Practical Retroduction. It is ordinarily called Presumption.