(3.) Opinion finds in a priori judgements no place whatever, for by them we either cognise something as quite certain or else cognise nothing at all. But if the given grounds of proof from which we start (as here from the purposes in the world) are empirical, then we cannot even with their aid form any opinion as to anything beyond the world of sense, nor can we concede to such venturesome judgements the smallest claim to probability. For probability is part of a certainty possible in a certain series of grounds (its grounds compare with the sufficient ground as parts with a whole), the insufficient ground of which must be susceptible of completion. But since, as determining grounds of one and the same judgement, they must be of the same kind, for otherwise they would not together constitute a whole (such as