— 562 —
Chapter IV

Of the Reality of our Knowledge.

Objection, Knowledge placed in Ideas may be all bare vision.
      §1. I Doubt not but my Reader, by this time, may be apt to
think, that I have been all this while only building a Castle in the
Air; and be ready to say to me, To what purpose all this stir?
Knowledge, say you, is only the perception of the agreement or
disagreement of our own Ideas: but who knows what those Ideas
may be? Is there any thing so extravagant, as the Imaginations of
Men’s Brains? Where is the Head that has no Chimeras in it? Or if
there be a sober and a wise Man, what difference will there be, by
your Rules, between his Knowledge, and that of the most extrava-
gant Fancy in the World? They both have their Ideas, and perceive
their agreement and disagreement one with another. If there be
any difference between them, the advantage will be on the warm-
headed Man’s side, as having the more Ideas, and the more lively.
— 563 —
And so, by your Rules, he will be the more knowing. If it be true,
that all Knowledge lies only in the perception of the agreement or
disagreement of our own Ideas, the Visions of an Enthusiast, and the
Reasonings of a sober Man, will be equally certain. ’Tis no matter
how Things are: so a Man observe but the agreement of his own
Imaginations, and talk conformably, it is all Truth, all Certainty.
Such Castles in the Air, will be as strong Holds of Truth, as the
Demonstrations of Euclid. That an Harpy is not a Centaur, is by
this way as certain knowledge, and as much a Truth, as that a
Square is not a Circle.
      But of what use is all this fine Knowledge of Mens own Imaginations,
to a Man that enquires after the reality of Things? It matters not
what Men’s Fancies are, ’tis the Knowledge of things that is only
to be prized: ’tis this alone gives a value to our Reasonings, and
preference to one Man’s Knowledge over another’s,
Locke Hum IV, 4, §1, pp. 562-563