Jean Buridan (ca. 1301 to ca. 1359 – 62) Buridan was a French priest, philosopher and scientist who taught at the University of Paris. His greatest achievement was the concept of “impetus,” which was a forerunner of the modern concept of “momentum.” Aristotle had taught that an object would move only if moved by an external force, so that a projectile (for example, an arrow) must be pushed along by the air through which it moves. A brilliant 6th-century Christian thinker named Philoponus proposed, on the contrary, that projectiles were moved by an “incorporeal motive power” that was imparted to them when they were launched (in the case of an arrow, for instance, by a bowstring). But Philoponus had suggested that this motive power gradually wore off. Buridan's ideas were a significant advance on those of Philoponus. He proposed that the quantity of “impetus” in a body remains constant, as long as the body’s motion is not impeded (as for example by the resistance of the medium through which it moves). Buridan also suggested that the impetus of a body is greater if the body is more massive and moving faster. Perhaps the only difference (if it is a difference) with the modern concept of momentum, is that Buridan saw impetus as a cause of motion, whereas today momentum is seen as a measure or concomitant of motion. Buridan was the teacher of an even more brilliant pupil, Bishop Nicolas Oresme, who carried his ideas about physics even further and made contributions to mathematics and many other fields.
Buridan’s philosohical ideas were also influential. He emphasized the importance of first seeking natural explanations for new or surprising phenomena:
“[Scientists explain such marvels] by appropriate natural causes; but common folk, not knowing of causes, believe these phenomena are produced by a miracle of God, which is usually not true.”