cause in impenetrability, in the collision of bodies, etc. Consequently both can be authenticated by means of an empirical intuition, i.e. the thought of them can be proved (demonstrated, verified) by an example; and this must be possible, for otherwise we should not be certain that the concept was not empty, i.e. devoid of any Object.

In Logic we ordinarily use the expressions demonstrable or indemonstrable only in respect of propositions, but these might be better designated by the titles respectively of mediately and immediately certain propositions; for pure Philosophy has also propositions of both kinds, i.e. true propositions, some of which are susceptible of proof and others not. It can, as philosophy, prove them on a priori grounds, but it cannot