s defined by Sir Isaac Newton to be a passive principle by which bodies persist in a state of motion or of rest, receive motion in proportion to the force impressing it, and resist as much as they are resisted. It is also defined by the same author to be a power implanted in all matter, whereby it resists any change endeavoured to be made in its state. See Physics.

IN ESSE is applied to things which are actually existing. Authors make a difference between a thing in esse, and a thing in posse. A thing that is not, but may be, they say is in posse, or potentia; but a thing apparent and visible, they say is in esse, that is, it has a real being eo instanti, whereas the other is casual, and at best but a possibility.