After Locke has pre-supposed experience， he goes on to say that it is the understanding which now discovers and desires the universal - the complex ideas. The Bishop of Worcester made the objection that “If the idea of substance be grounded upon plain and evident reason， then we must allow an idea of substance which comes not in by sensation or reflection.” Locke replies：
“General ideas come not into the mind by sensation or reflection， but are the creatures or inventions of the understanding. The mind makes them from ideas which it has got by sensation and reflection.” The work of the mind now consists in bringing forth from several simple so-called ideas a number of new ones， by means of its working upon this material through comparing， distinguishing and contrasting it， and finally through separation or abstraction， whereby the universal conceptions， such as space， time， existence， unity and diversity， capacity， cause and effect， freedom， necessity， take their rise. “The mind in respect of its simple ideas is wholly passive， and receives them all from the existence and operation of things， such as sensation or reflection offers them， without being able to make any one idea.” But “the mind often exercises an active power in making these several combinations. For it being once furnished with simple ideas it can put them together in several combinations.” According to Locke therefore thought itself is not the essence of the soul， but one of its powers and manifestations. He maintains thought to be existent in consciousness as conscious thought， and thus brings it forward as a fact in his experience， that we do not always think. Experience demonstrates dreamless sleep when the sleep is profound. Locke quotes the example of a man who remembered no dream until he had reached his twenty-fifth year. It is as in the Xenien， - (6)Oft schon war ich， und hab' wirklich an gar nichts gedacht.
That is to say， my object is not a thought. But sensuous perception and recollection are thought， and thought is truth.(7) Locke， however， places the reality of the understanding only in the formal activity of constituting new determinations from the simple conceptions received by means of perception， through their comparison and the combination of several into one； it is the apprehension of the abstract sensations which are contained in the objects. Locke likewise distinguishes (Bk. 11. chap. xi. § 15-17) between pure and mixed modes. Pure modes are simple determinations such as power， number， infinitude； in such expressions as causality we reach， on the other hand， a mixed mode.
Locke now explains in detail the manner in which the mind， from the simple ideas of experience， reaches more complex ideas； but this derivation of general determinations from concrete perception is most unmeaning， trivial， tiresome and diffuse； it is entirely formal， an empty tautology.
For instance we form the general conception of space from the perception of the distance of bodies by means of sight and feeling.(8) Or in other words， we perceive a definite space， abstract from it， and then we have the conception of space generally； the perception of distances gives us conceptions of space. This however is no deduction， but only a setting aside of other determinations； since distance itself is really space， mind thus determines space from space.
Similarly we reach the notion of time through the unbroken succession of conceptions during our waking moments，(9) i.e，. from determinate time we perceive time in general. Conceptions follow one another in a continual succession； if we set aside the particular element that is present we thereby receive the conception of time. Substance (which Locke does not accept in so lofty a sense as Spinoza)， a complex idea， hence arises from the fact that we often perceive simple ideas such as blue， heavy， etc.， in association with one another. This association we represent to ourselves as something which so to speak supports these simple ideas， or in which they exist.(10)Locke likewise deduces the general conception of power.(11) The determinations of freedom and necessity， cause and effect， are then derived in a similar way. “In the notice that our senses take of the constant vicissitude of things， we cannot but observe， that several particulars， both qualities and substance， begin to exist； and that they receive this their existence from the due application and operation of some other being. From this observation we get our ideas of cause and effect，”
for instance when wax is melted by the fire.(12) Locke goes on to say： “Every one， I think， finds in himself a power to begin or forbear， continue or put an end to several actions in himself. From the consideration of the extent of this power of the mind over the actions of the man， which every one finds in himself， arise the ideas of liberty and necessity.”(13)We may say that nothing can be more superficial than this derivation of ideas. The matter itself， the essence， is not touched upon at all. A determination is brought into notice which is contained in a concrete relationship； hence the understanding on the one hand abstracts and on the other establishes conclusions. The basis of this philosophy is merely to be found in the transference of the determinate to the form of universality， but it was just this fundamental essence that we had to explain. As to this Locke confesses of space， for example， that he does not know what it really is.(14) This so-called analysis by Locke of complex conceptions， and his so-called explanation of the same， has， on account of its uncommon clearness and lucidity of expression， found universal acceptance. For what can be clearer than to say that we have the notion of time because we perceive time， if we do not actually see it， and that we conceive of space because we see it？ The French have accepted this most readily and they have carried it further still； their Idéologie contains nothing more nor less.
