ent 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. Fourthly, Of real Existence agreeing to any idea.

FOURTHLY, The fourth and last sort is that of ACTUAL REAL EXISTENCE
agreeing to any idea.

Within these four sorts of agreement or disagreement is, I suppose,
contained all the knowledge we have, or are capable of. For all the
inquiries we can make concerning any of our ideas, all that we know or
can affirm concerning any of them, is, That it is, or is not, the same
with some other; that it does or does not always co-exist with some
other idea in the same subject; that it has this or that relation with
some other idea; or that it has a real existence without the mind. Thus,
'blue is not yellow,' is of identity. 'Two triangles upon equal bases
between two parallels are equal,' is of relation. 'Iron is susceptible
of magnetical impressions,' is of co-existence. 'God is,' is of real
existence. Though identity and co-existence are truly nothing but
relations, yet they are such peculiar ways of agreement or disagreement
of our ideas, that they deserve well to be considered as distinct heads,
and not under relation in general; since they are so different grounds
of affirmation and negation, as will easily appe