He drew inspiration from many scientists that came before him, most notably Galileo Galilei and Rene Descartes. The First Law of Motion pertained to inertia, the Second Law of Motion explained the principles behind acceleration, and the Third Law of Motion asserted that every force was accompanied by an equal and opposite force. Collectively known as the Philosophiæ Naturalis Principia Mathematica, where he explained what he called the Three Laws of Motion.