...and that the number of them is what we have stated. The number is the same as that of the things comprehended wunder the question 'why'. The 'why' is referred ultimately either (1) in things which do not involve motion, e.g. in mathematics, to the 'what' (to the difinition of 'straight line' or commensurable', &c.), or (2) to what initiated a motion, e.g. 'why did they go to war?- because there had been a raid'; or (3) we are inquiring 'for the sake of what?' -- 'that they may rule'; or (4), in the case of things that come in to being, we looking for the matter. The causes, therefore, are these and so many in number.
the matter, the form, the mover, 'that for the sake of which'
from Aristotle 'Physics' Bk. II: Ch. 7