Leibniz thus succeeds in avoiding two errors into which philosophers whose general aims are much like his have fallen. One is dividing _a priori_ and _a posteriori_ truths from each other by a hard and fixed line, so that we are conceived to have some knowledge which comes wholly from experience, while there is another which comes wholly from reason. According to Leibniz, there is no thought so abstract that it does not have its connection with a sensible experience, or rather its embodiment in it. And, on the other hand, there is no experience so thoroughly sensuous that it does not bear in itself traces of its origin in reason. "_All_ our thoughts come from the depths of the soul," says Leibniz; there are none that "come" to us from without. The other error is the interpretation of the existence of innate ideas or "intuitions" (as this school generally calls them) in a purely formal sense. They are thus considered as truths contained in and somehow expressed by intelligence, but yet not so connected with it that in knowing them we necessarily know intelligence itself. They are considered rather as arbitrary determinations of truths by a power whose own nature is conceivably foreign to truth, than as so many special developments of an activity which may indifferently be called "intelligence" or "truth." Leibniz, however, never fails to state that an innate truth is, after all, but one form or aspect of the activity of the mind in knowing. In this way, by bringing to light a deeper and richer conception of what in reality constitutes an innate idea, Leibniz answers Locke. His reply is indirect; it consists rather in throwing a flood of new light upon the matter discussed, than in a ponderous response and counter-attack. But when Leibniz touches upon the conception of a _tabula rasa_, of a mind which in itself is a mere blank, but has the capacity for knowing, he assumes the offensive. The idea of a bare capacity, a formal faculty, of power which does not already involve some actual content within itself, he repudiates as a relic of scholasticism. What is the soul, which has nothing until it gets it from without? The doctrine of a vacuum, an emptiness which is real, is always absurd; and it is doubly so when to this vacuum is ascribed powers of feeling and thinking, as Locke does. Accepting for the moment the metaphor of a _tabula rasa_, Leibniz asks where we shall find a tablet which yet does not have some quality, and which is not a co-operating cause, at least, in whatever effects are produced upon it? The notion of a soul without thought, an empty tablet of the soul, he says, is one of a thousand fictions of philosophers. He compares it with the idea of "space empty of matter, absolute uniformity or homogeneity, perfect spheres of the second element produced by primordial perfect cubes, abstractions pure and simple, to which our ignorance and inattention give birth, but of which reality does not