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Nor will it be less true or certain, because moral Ideas are of our own making and naming.
      §9. But it will here be said, that if moral Knowledge be placed in
the Contemplation of our own moral Ideas, and those, as other Modes,
be of our own making, What strange Notions will there be of
Justice and Temperance? What confusion of Vertues and Vices, if
every one may make what Ideas of them he pleases? No confusion
nor disorder in the Things themselves, nor the Reasonings about
them; no more than (in Mathematicks) there would be a Disturb-
ance in the Demonstration, or a change in the Properties of Figures,
and their Relations one to another, if a Man should make a Triangle
with four Corners, or a Trapezium with four right Angles: that is, in
plain English, change the Names of the Figures, and call that by one
Name, which Mathematicians call’d ordinarily by another. For let
a Man make to himself the Idea of a Figure with three Angles,
— 567 —
whereof one is a right one, and call it, if he please, Equilaterum or
Trapezium, or any thing else, the Properties of, and Demonstrations
about that Idea, will be the same, as if he call’d it a Rectangular-
Triangle. I confess, the change of the Name, by the impropriety of
Speech, will at first disturb him, who knows not what Idea it
stands for: but as soon as the Figure is drawn, the Consequences
and Demonstration are plain and clear. Just the same is it in moral
Knowledge, let a Man have the Idea of taking from others, without
their Consent, what their honest Industry has possessed them of,
and call this Justice, if he please. He that takes the Name here
without the Idea put to it, will be mistaken, by joining another Idea
of his own to that Name: But strip the Idea of that Name, or take it
such as it is in the Speaker’s Mind, and the same Things will agree
to it, as if you call’d it Injustice. Indeed, wrong Names in moral
Discourses, breed usually more disorder, because they are not so
easily rectified, as in Mathematicks, where the Figure once drawn
and seen, makes the Name useless and of no force. For what need
of a Sign, when the Thing signified is present and in view? But in
moral Names, that cannot be so easily and shortly done, because of
the many decompositions that go to the making up the complex
Ideas of those Modes. But yet for all this the miscalling of any of
those Ideas, contrary to the usual signification of the Words of that
Language, hinders not, but that we may have certain and demon-
strative Knowledge of their several Agreements and Disagreements,
if we will carefully, as in Mathematicks, keep to the same precise
Ideas, and trace them in their several Relations one to another,
without being led away by their Names. If we but separate the
Idea under consideration from the Sign that stands for it, our Know-
ledge goes equally on in the discovery of real Truth and Certainty,
whatever Sounds we make use of.
Locke Hum IV, 4, §9, pp. 566-567