— 534 —
Demonstration not limited to quantity.
      §9. It has been generally taken for granted, that Mathematicks
alone are capable of demonstrative certainty: But to have such an
agreement or disagreement, as may intuitively be perceived, being,
as I imagine, not the privilege of the Ideas of Number, Extension, and
Figure alone, it may possibly be the want of due method, and
application in us; and not of sufficient evidence in things, that
Demonstration has been thought to have so little to do in other
parts of Knowledge, and been scarce so much as aim’d at by any
but Mathematicians. For whatever Ideas we have, wherein the
Mind can perceive the immediate agreement or disagreement that
is between them, there the Mind is capable of intuitive Knowledge;
— 535 —
and where it can perceive the agreement or disagreement of any two
Ideas, by an intuitive perception of the agreement or disagreement
they have with any intermediate Ideas, there the Mind is capable of
Demonstration, which is not limited to Ideas of Extension, Figure,
Number, and their Modes.
Locke Hum IV, 2, §9, pp. 534-535