=This term a priori is not yet definite enough.=[216]--It is frequently employed in a merely relative sense. Thus we can say of a person who undermines the foundations of his house that he might have known _a priori_ that it would collapse, that is, that he need not wait for the experience of its actual fall. But still he could not know this entirely _a priori_; he had first to learn from experience that bodies are heavy, and will fall when their supports are taken away. But as dealt with in the _Critique_ the term _a priori_ is used in an absolute sense, to signify that knowledge which is independent, not of this or that experience only, but of all impressions of the senses. Thus far Kant’s position is comparatively clear; but he proceeds to distinguish two forms within the absolutely _a priori_, namely, mixed and pure. The absolutely _a priori_ is mixed when it contains an empirical element, pure when it does not. (“Pure” is no longer taken in the meaning which it has in the title of the section.[217] It signifies not the _a priori_ as such, but only one subdivision of it.) Thus after defining absolutely _a priori_ knowledge as independent of all experience, Kant takes it in one of its forms as involving empirical elements. The example which he gives of an absolutely _a priori_ judgment, which yet is not pure, is the principle: every change has its cause. “Change” is an empirical concept, but the synthetic relation asserted is absolutely _a priori_. In the next section[218] this same proposition is cited as a _pure_ judgment _a priori_--“pure” being again used in its more general meaning as synonymous with _a priori_. This confusion results from Kant’s exclusive preoccupation with the _a priori_, and consequent failure to give due recognition to the correlative problem of the empirical judgment. The omitted factor retaliates by thus forcing its way into Kant’s otherwise clean-cut divisions. Also, it is not true that the relative _a priori_ falls outside the sphere of the Critical enquiry. Such judgment expresses necessity or objectivity, and for that reason demands a transcendental justification no less urgently than the absolutely _a priori_. The finding of such justification is, indeed, the central problem of the _Analytic_.[219] The subdivisions of the _a priori_ may be tabulated thus: { Relative, _e.g._ every unsupported house must { fall. _A priori_ knowledge{ { Mixed, _e.g._ every change has its cause. { Absolute { Pure, _e.g._ a straight line is the shortest { { distance between two points.