God who gave Animals self motion beyond our understanding is without doubt able to implant other principles of motion in bodies [which] we may understand as little. Some would readily grant this may be a Spiritual one; yet a mechanical one might be showne, did not I think it better to pass it by.

Every action has an equal and opposite reaction

The seed of a tree has the nature of a branch or twig or bud. It is a part of the tree, but if separated and set in the earth to be better nourished, the embryo or young tree contained in it takes root and grows into a new tree.

I feign no hypotheses.

A man may imagine things that are false, but he can only understand things that are true, for if the things be false, the apprehension of them is not understanding.

Thus far I have explained the phenomena of the heavens and of our sea by the force of gravity, but I have not yet assigned a cause to gravity. Indeed, this force arises from some cause that penetrates as far as the centers of the sun and planets without any diminution of its power to act, and that acts not in proportion to the quantity of the surfaces of the particles on which it acts (as mechanical causes are wont to do) but in proportion to the quantity of solid matter, and whose action is extended everywhere to immense distances, always decreasing as the squares of the distances.

The best way to understanding is a few good examples.