=57.= We may retain, however, a distinction roughly corresponding to the Kantian _à priori_ and _à posteriori_, though less rigid, and more liable to change with the degree of organisation of knowledge. Kant usually endeavoured to prove, as observed above, that his synthetic _à priori_ propositions were necessary prerequisites of experience; now although we cannot retain the term synthetic, we can retain the term _à priori_, for those assumptions, or those postulates, from which alone the possibility of experience follows. Whatever can be deduced from these postulates, without the aid of the matter of experience, will also, of course, be _à priori_. From the standpoint of general logic, the laws of thought and the categories, with the indispensable conditions of their applicability, will be alone _à priori_; but from the standpoint of any special science, we may call _à priori_ whatever renders possible the experience which forms the subject-matter of our science. In Geometry, to particularize, we may call _à priori_ whatever renders possible experience of externality as such. It is to be observed that this use of the term is at once more rationalistic and less precise than that of Kant. Kant would seem to have supposed himself immediately aware, by inspection, that some knowledge was apodeictic, and its subject-matter, therefore, _à priori_: but he did not always deduce its apriority from any further principle. Here, however, it is to be shown, before admitting apriority, that the falsehood of the judgment in question would not be effected by a mere change in the _matter_ of experience, but only by a change which should render some branch of experience formally impossible, _i.e._ inaccessible to our methods of cognition. The above use is also less precise, for it varies according to the specialization of the experience we are assuming possible, and with every progress of knowledge some new connection is perceived, two previously isolated judgments are brought into logical relation, and the _à priori_ may thus, at any moment, enlarge its sphere, as more is found deducible from fundamental postulates.