  In terms of this threefold division it is the duty of the entity effecting change to confer the requisite form on the object changed, as Physics 3.2, 202a9–11 puts it. But there are further important requirements for such a change to occur. First of all, these motions or changes occur at the interaction of two potentialities. One, the passive potentiality, is in the object undergoing change, while the other, the active potentiality, is in the entity initiating change.  The two potentialities need to match each other: when there is a potentiality for being heated in the object undergoing change, the process needs to be initiated by another object possessing an active potentiality for effecting the heating. This is true to the extent that Aristotle can claim that the definition of passive potentiality is dependent on that of the active potentiality (Metaphysics 9.1, 1046a9–13). These two potentialities need to work in tandem, and consequently Aristotle can claim that there is only a single process going on, which is located in the entity moved. Thus, for example, when a process of instruction is going on, it is identical to a process of knowledge acquisition, which happens in the mind of the learner. Hence although action and passion retain their categorical difference, because their accounts are different, what they subsist in, the motion, will be the same (Physics 3.3,  202b19–22).[21] 