9. Modern definitions of motion.
Nor have the modern philosophers, who have endeavoured to throw off the
jargon of the schools, and speak intelligibly, much better succeeded in defining simple ideas, whether by
explaining their causes, or any otherwise. The atomists, who define motion to be "a passage from one 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, etc.?
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.
