An Essay Concerning Human Understanding / Ein Versuch über den menschlichen Verstand. Auswahlausgabe. John Locke

has been shewn, certain Collections of simple Ideas, that have been observed or supposed constantly to exist together. But such a complex Idea cannot be the real Essence of any Substance; for then the Properties we discover in that Body, would depend on that complex Idea, and be deducible from it, and their necessary connexion with it be known; as all Properties of a Triangle depend on, and as far as they are discoverable, are deducible from the complex Idea of three Lines, including a Space. But it is plain, that in our complex Ideas of Substances, are not [374]contained such Ideas, on which all the other Qualities, that are to be found in them, do depend. […]

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      § 8. Secondly, Those who, neglecting that useless Supposition of unknown real Essences, whereby they are distinguished, endeavour to copy the Substances, that exist in the World, by putting together the Ideas of those sensible Qualities, which are found co-existing in them, though they come much nearer a likeness of them, than those who imagine, they know not what real specifick Essences; yet they arrive not at perfectly adequate Ideas of those Substances […]. The simple Ideas whereof we make our complex ones of Substances, are all of them (bating only the Figure and Bulk of some sorts) Powers; which being Relations to other Substances, we can never be sure that we know all the Powers, that are in any one Body, till we have tried what Changes it is fitted to give to, or receive from other Substances, in their several ways of application: which being impossible to be tried upon any one Body, much less upon all, it is impossible we should have adequate Ideas of any Substance, made up of a Collection of all its Properties.

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      § 12. Thus the Mind has three sorts of abstract Ideas, or nominal Essences:

      First, Simple Ideas, which are ἔκτυπα, or Copies; but yet certainly adequate. Because being intended to express nothing but the power in Things to produce in the Mind such a [376]Sensation, that Sensation, when it is produced, cannot but be the Effect of that Power. […]

      § 13. Secondly, The complex Ideas of Substances are Ectypes, Copies too; but not perfect ones, not adequate: Which is very evident to the Mind, in that it plainly perceives, that whatever Collection of simple Ideas it makes of any Substance that exists, it cannot be sure, that it exactly answers all that are in that Substance. […]

      § 14. Thirdly, Complex Ideas of Modes and Relations, are Originals, and Archetypes; are not Copies, nor made after the Pattern of any real Existence, to which the Mind intends them to be conformable, and exactly to answer. […] The Ideas therefore of Modes and Relations, cannot but be adequate.

       CHAPTER XXXII

      Of True and False Ideas

      § 1. THOUGH Truth and Falshood belong, in Propriety of Speech, only to Propositions; yet Ideas are oftentimes termed true or false […]. Though, I think, that when Ideas themselves are termed true or false, there is still some secret or tacit Proposition, which is the Foundation of that Denomination: as we shall see, if we examine the particular Occasions, wherein they come to be called true or false. In all which, we shall find some kind of Affirmation, or Negation, which is the Reason of that Denomination. For our Ideas, being nothing but bare Appearances or Perceptions in our Minds, cannot properly and simply [378]in themselves be said to be true or false, no more than a single Name of any thing, can be said to be true or false.

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      § 3. […] For Truth or Falshood, lying always in some Affirmation, or Negation, Mental or Verbal, our Ideas are not capable any of them of being false, till the Mind passes some Judgment on them; that is, affirms or denies something of them.

      § 4. When-ever the Mind refers any of its Ideas to any thing extraneous to them, they are then capable to be called true or false. Because the Mind in such a reference, makes a tacit Supposition of their Conformity to that Thing: which Supposition, as it happens to be true or false; so the Ideas themselves come to be denominated. The most usual Cases wherein this happens, are these following:

      § 5. First, When the mind supposes any Idea it has, conformable to that in other Men’s Minds called by the same common Name; v. g. when the Mind intends, or judges its Ideas of Justice, Temperance, Religion, to be the same, with what other Men give those Names to.

      Secondly, When the Mind supposes any Idea it has in it self, to be conformable to some real Existence. Thus the two Ideas, of a Man, and a Centaur, supposed to be the Ideas of real Substances, are the one true, and the other false