Thus this Earth resembles a great animall or rather an inanimate vegetable, draws in aethereal breath for its dayly refreshment and vitall ferment and transpires again grosses exhalations. And, according to the condition of all other things living, ought to have its time of beginning, youth, old age and perishing.

Where both are friends, it is right to prefer truth.

As in Mathematicks, so in Natural Philosophy, the Investigation of difficult Things by the Method of Analysis, ought ever to precede the Method of Composition. This Analysis consists in making Experiments and Observations, and in drawing general Conclusions from them by Induction, and admitting of no Objections against the Conclusions, but such as are taken from Experiments, or other certain Truths. For Hypotheses are not to be regarded in experimental Philosophy.

Nature is very consonant and conformable with herself.

The Ignis Fatuus is a vapor shining without heat.

I do not know what I may appear to the world, but to myself I seem to have been only a boy playing on the seashore.

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.