In reason man possesses reflection or self-consciousness as well as the knowledge of God, of the universal, and of the eternal truths or a priori knowledge, while the animal is limited in its perception to experience, and in its reasoning to the connection of perceptions in accordance with memory.  Man differs from higher beings in that the majority of his ideas are confused.  Under confused ideas Leibnitz includes both sense-perceptions—­anyone who has distinct ideas alone, as God, has no sense-perceptions—­and the feelings which mediate between the former and the perfectly distinct ideas of rational thought.  The delight of music depends, in his opinion, on an unconscious numbering and measuring of the harmonic and rhythmic relations of tones, aesthetic enjoyment of the beautiful in general, and even sensuous pleasure, on the confused perception of a perfection, order, or harmony.

The application of the lex continui to the inner life has a very wide range.  The principal results are:  (1) the mind always thinks; (2) every present idea postulates a previous one from which it has arisen; (3) sensation and thought differ only in degree; (4) in the order of time, the ideas of sense precede those of reason.  We are never wholly without ideas, only we are often not conscious of them.  If thought ceased in deep sleep, we could have no ideas on awakening, since every representation proceeds from a preceding one, even though it be unconscious.

In the thoughtful New Essays concerning the Human Understanding Leibnitz develops his theory of knowledge in the form of a polemical commentary to Locke’s chief work.[1] According to Descartes some ideas (the pure concepts) are innate, according to Locke none, according to Leibnitz all.  Or:  according to Descartes some ideas (sensuous perceptions) come from without, according to Locke all do so, according to Leibnitz none.  Leibnitz agrees with Descartes against Locke in the position that the mind originally possesses ideas; he agrees with Locke against Descartes, that thought is later than sensation and the knowledge of universals later than that of particulars.  The originality which Leibnitz attributes to intellectual ideas is different from that which Descartes had ascribed and Locke denied to them.  They are original in that they do not come into the soul and are not impressed upon it from without; they are not original in that they can develop only from previously given sense-ideas; again, they are original in that they can be developed from confused ideas only because they are contained in them implicite or as pre-dispositions.  Thus Leibnitz is able to agree with both his predecessors up to a certain point:  with the one, that the pure concepts have their origin within the mind; with the other, that they are not the earliest knowledge, but are conditioned by sensations.  This synthesis, however, was possible only because Leibnitz looked on sensation differently from both the others.