— 527 —
Fourthly, of real Existence.
      §7. 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 Enquiries that we can make, concern-
ing 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 to 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 Basis, 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 so 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 appear to any one, who will but reflect on
what is said in several places of this Essay. I should now proceed to
examine the several degrees of our Knowledge, but that it is neces-
sary first, to consider the different acceptations of the word
Knowledge.
Locke Hum IV, 1, §7, p. 527