 Chapter 3 of Aristotle’s Physics II is a treatise on the subject of the four causes and it corresponds almost entirely to Metaphysics V.2. Then chapters 4 and 5 examine the question of chance and incidental causation, i.e., spontaneity. The question is related to whether Nature acts with purpose and Averroes sees its great significance. Commenting on 196b10–17, Averroes enters into a discussion with Avicenna on the status of two irregular kinds of causation, fortuna and casus, chance (LC f. 66D–67D TC48). In the Arabic translation of the Physics they were bakht and min tilqā’ al-nafs (Aristotle, Ṭabīʻa [1964: 111: 4–5]), and in Averroes’ short commentary, bakht and ittifāq, respectively (SC 26: 19). Averroes formulates the Aristotelian argument in the form of a conditional syllogism the conclusion of which is that spontaneous causation happens in things that are possible only in a few cases, in minori parte. Avicenna argues that the same action can be necessarily caused in some beings and accidentally in some others and that, in a similar way, the action can be possible for some beings in most cases and for some others in the least cases. Averroes gives an example of walking and resting. According to Avicenna, walking is accidental from the point of view of the moving power, but it is necessary from that of the desire.