Conatus - Medieval Views

Medieval Views

Further information: Theory of impetus See also: Physics in medieval Islam, Scholasticism, and Medieval philosophy

There is a traditional connection between conatus and motion itself. Aquinas and Abravanel (1265–1321) both related the concept directly to that which Augustine (354–430 CE) saw to be the "natural movements upward and downward or with their being balanced in an intermediate position" described in his De Civitate Dei, (c. 520 CE). They called this force that causes objects to rise or fall, "amor naturalis", or "natural love".

In the 6th century, John Philoponus (c. 490–c. 570 CE) criticized Aristotle's view of motion, noting the inconsistency between Aristotle's discussion of projectiles, where the medium of aether keeps projectiles going, and his discussion of the void, where there is no such medium and hence a body's motion should be impossible. Philoponus proposed that motion was not maintained by the action of some surrounding medium but by some property, or conatus implanted in the object when it was set in motion. This was not the modern concept of inertia, for there was still the need for an inherent power to keep a body in motion. This view was strongly opposed by Averroës and many scholastic philosophers who supported Aristotle. The Aristotelian view was also challenged in the Islamic world. For example, Ibn al-Haytham (Alhazen) seems to have supported Philoponus' views, while he developed a concept similar to inertia. The concept of inertia was developed more clearly in the work of his contemporary Avicenna, who conceived a permanent force whose effect is dissipated only as a result of external agents such as air resistance, making him "the first to conceive such a permanent type of impressed virtue for non-natural motion." Avicenna's concept of mayl is almost the opposite of the Aristotelian conception of violent motion and is reminiscent of Newton's first law of motion. Avicenna also developed an idea similar to momentum, when he attempted to provide a quantitive relation between the weight and velocity of a moving body.

Jean Buridan (1300–1358) also rejected the notion that this motion-generating property, which he named impetus, dissipated spontaneously. Buridan's position was that a moving object would be arrested by the resistance of the air and the weight of the body which would oppose its impetus. He also maintained that impetus increased with speed; thus, his initial idea of impetus was similar in many ways to the modern concept of momentum. Despite the obvious similarities to more modern ideas of inertia, Buridan saw his theory as only a modification to Aristotle's basic philosophy, maintaining many other peripatetic views, including the belief that there was still a fundamental difference between an object in motion and an object at rest. Buridan also maintained that impetus could be not only linear, but also circular in nature, causing objects such as celestial bodies to move in a circle.