This then is the first agreement or disagreement which the mind perceives in its ideas; which it always perceives at first sight: and if there ever happen any doubt about it, it will always be found to be about the names, and not the ideas themselves, whose identity and diversity will always be perceived, as soon and clearly as the ideas themselves are; nor can it possibly be otherwise.
5.

Secondly, Of abstract Relations between ideas.
SECONDLY, the next sort of agreement or disagreement the mind perceives in any of its ideas may, I think, be called RELATIVE, and is nothing but the perception of the RELATION between any two ideas, of what kind soever, whether substances, modes, or any other.

For, since all distinct ideas must eternally be known not to be the same, and so be universally and constantly denied one of another, there could be no room for any positive knowledge at all, if we could not perceive any relation between our ideas, and find out the agreement or disagreement they have one with another, in several ways the mind takes of comparing them.
6.

Thirdly, Of their necessary Co-existence in Substances.
THIRDLY, The third sort of agreement or disagreement to be found in our ideas, which the perception of the mind is employed about, is CO-EXISTENCE or NON-CO-EXISTENCE in the SAME SUBJECT; and this belongs particularly to substances.

Thus when we pronounce concerning gold, that it is fixed, our knowledge of this truth amounts to no more but this, that fixedness, or a power to remain in the fire unconsumed, is an idea that always accompanies and is joined with that particular sort of yellowness, weight, fusibility, malleableness, and solubility in AQUA REGIA, which make our complex idea signified by the word gold.
7.