Every body persists in a state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces having impact upon it.
Isaac NewtonGravity explains the motions of the planets, but it cannot explain who sets the planets in motion.
Isaac NewtonGod is able to create particles of matter of several sizes and figures and perhaps of different densities and forces, and thereby to vary the laws of nature, and make worlds of several sorts in several parts of the Universe.
Isaac NewtonGod 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.
Isaac NewtonThus 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.
Isaac Newton