In the 12th century, Hibat Allah Abu'l-Barakat al-Baghdaadi adopted and modified Avicenna's theory on projectile motion. In his "Kitab al-Mu'tabar", Abu'l-Barakat stated that the mover imparts a violent inclination ("mayl qasri") on the moved and that this diminishes as the moving object distances itself from the mover. According to Shlomo Pines, al-Baghdaadi's theory of motion was "the oldest negation of Aristotle's fundamental dynamic law that a constant force produces a uniform motion, is thus an anticipation in a vague fashion of the fundamental law of classical mechanics that a force applied continuously produces acceleration." The same century, Ibn Bajjah proposed that for every force there is always a reaction force. While he did not specify that these forces be equal, it is still an early version of the third law of motion which states that for every action there is an equal and opposite reaction.