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146 perceived, and that not accidentally. But there are appearances which are fallacious, although our conception of them at the time may be true, as the sun, for instance, appears to be a foot in diameter, and yet we are satisfied that it is larger than the earth; and in such a case it happens either that the true opinion of the sun's dimension must have been cast aside, or else, while the sun remains as it was and the true opinion has neither been forgotten nor changed, that the opinion is at once both true and false. But the opinion is simply false when it escapes us that the thing seen is altered. It is evident, then, that imagination can neither be any one, nor be derived from any one of those faculties.

Since one object having been set in motion can communicate motion to another, and since imagination seems to be a kind of motion, and never to be produced without sensation, or in other than sentient creatures, or without the objects of sentient perception, and since, on the other hand, motion can be produced by the act of sensation, and this motion must of necessity be equal to the impression, it may be admitted that the motion of imagination can neither be produced without sensation, nor in other than sentient beings; that beings endowed with it act and are acted upon in many ways, and that its manifestations are both true and false. This latter alternative happens thus: the sensation which is derived from the objects peculiar