place to another,' what do they more than put one synonymous word for
another? For what is PASSAGE other than MOTION? And if they were asked
what passage was, how would they better define it than by motion? For is
it not at least as proper and significant to say, Passage is a motion
from one place to another, as to say, Motion is a passage, &c.? This is
to translate, and not to define, when we change two words of the same
signification one for another; which, when one is better understood than
the other, may serve to discover what idea the unknown stands for; but
is very far from a definition, unless we will say every English word in
the dictionary is the definition of the Latin word it answers, and that
motion is a definition of MOTUS. Nor will 'the successive application of
the parts of the superficies of one body to those of another,' which the
Cartesians give us, prove a much better definition of motion, when well
examined.


10. Definitions of Light.

'The act of perspicuous, as far forth as perspicuous,' is another
Peripatetic definition of a simple idea; which, though not more
absurd than the former of motion, yet betrays its uselessness and
insignificancy more plainly; because experience will easily convince any
one that it cannot make the meaning of the word LIGHT (which it pretends
to define) at all understood by a blind man, but the definition of
motion appears not at first sight so useless, because it escapes this
way of trial. For this simple idea, entering by the touch as well as
sight, it is impossible to show an example of any one who has no other
way to get the idea of motion, but barely by the definition of that
name. Those who tell us that light is a great number of little globules,
striking briskly on the bottom of the eye, speak more intelligibly than