 Alexander develops the notion of stochastic technê further in his commentary on Aristotle’s Topics. Addressing the problem that dialectic does not always achieve its goal, i.e., leading the interlocutor to a contradiction, he divides technai into ones which achieve their ends by definite steps and those which cannot (In Top. 32,10–34,1). Given materials, tools, and other conditions, carpentry, e.g., can produce houses by following a series of steps each of which is effective in a determinate way. However, medicine does not always cure and certainly does not cure with the reliability that carpentry produces houses. Even though medicine tries everything in its power, chance can intervene so that it does not achieve its goal, the curing of the patient. When carpentry, by contrast, tries everything in its power, it achieves its goal. If there is failure, it is the result not of chance but of error in executing the technê, as Alexander says in Quaestiones (Quaestio 2.16, 10–25). To mark the difference between these two kinds of technê, Alexander says that the task (ergon) of medicine is to try everything possible to achieve its goal (telos); but achieving its goal is not (totally) within the power of medicine. He calls stochastic, then, the sorts of technê whose task is to try everything possible to achieve its goal, the realization of the goal being subject to chance.