The theory of impetus proposed that motion was maintained by some property of the body, imparted when it was set in motion. Buridan was the first to name this motion-maintaining property impetus but the theory itself probably did not originate with him. A less sophisticated notion of impressed forced can be found in the commentary of John Philoponus on Aristoteilan physics. In this he was possibly influenced by John Philoponus who was developing the Stoic notion of hormé (impulse). The major difference between Buridan's theory and that of his predecessor is that he rejected the view that the impetus dissipated spontaneously, instead asserting that a body would be arrested by the forces of air resistance and gravity which might be opposing its impetus. Buridan further held that the impetus of a body increased with the speed with which it was set in motion, and with its quantity of matter. This is closely related to the modern concept of momentum. Buridan saw impetus as causing the motion of the object: