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.

It is 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 strongholds 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 MEN'S OWN IMAGINATIONS, to a man that inquires after the reality of things?
It matters not what men's fancies are, it is the knowledge of things that is only to be prized: it is this alone gives a value to our reasonings, and preference to one man's knowledge over another's, that it is of things as they really are, and not of dreams and fancies.' 2.

Answer Not so, where Ideas agree with Things.
To which I answer, That if our knowledge of our ideas terminate in them, and reach no further, where there is something further intended, our most serious thoughts will be of little more use than the reveries of a crazy brain; and the truths built thereon of no more weight than the discourses of a man who sees things clearly in a dream, and with great assurance utters them.