  Third, the principle of causational synonymy is restricted to substances at the end of Metaphysics   7.9,[29]  and in the first half of the same chapter the non-standard presence of some causally relevant forms may also be envisaged.   Aristotle’s example there is the heat in  motion, which produces heat in the body when the doctor rubs the  patient in the appropriate manner. This heat in the motion can be  the presence of an active potentiality in the motion which is able  to elicit heat in the body, without heat being predicable of motion  itself.  But even if such non-inherential subsistence of properties  is not envisaged in this passage—the alternative being that the heat in motion is the heat in the skin of the patient, caused by the rub, which then enters into the inner recesses of the body, becoming heat in the body—some  similar sort of presence is required in two large classes of cases: natural generations and artificial productions. 