I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypotheses; for whatever is not deduced from the phenomena is to be called a hypothesis, and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy.

Absolute, true and mathematical time, of itself, and from its own nature flows equably without relation to anything external.

Do not Bodies and Light act mutually upon one another; that is to say, Bodies upon Light in emitting, reflecting, refracting and inflecting it, and Light upon Bodies for heating them, and putting their parts into a vibrating motion wherein heat consists?

I see I have made my self a slave to Philosophy.

Our present work sets forth mathematical principles of philosophy. For the basic problem of philosophy seems to be to discover the forces of nature from the phenomena of motions and then to demonstrate the other phenomena from these forces. It is to these ends that the general propositions in books 1 and 2 are directed, while in book 3 our explanation of the system of the world illustrates these propositions.

The qualities of bodies, which admit neither intension nor remission of degrees, and which are found to belong to fill bodies within the reach of our experiments, are to be esteemed the universal qualities of all bodies whatsoever.

The latest authors, like the most ancient, strove to subordinate the phenomena of nature to the laws of mathematics.