Donald Skilling's article on causes is an excellent introduction to the necessary study of causes. The article seems to follow Aristotle's writings in the Metaphysics (I, ch. 3) although strictly speaking Aristotle uses the word "essence" where the article uses "form" as the second of the four causes - presumably this is becuase Donald is following Thomas Taylor's note to this section which says "By essence Aristotle means form, for everything is that which it is though form."
There is, however, a further refinement to this analysis taught by the later Platonist of the Athenian Academy. It is a development which, I think, helps the philosopher understand why things arise in their particularity. Proclus (in Tim. I, 263, 20-30) and following him Olympiodorus (in Gorgiam. V, 1-31) give six causes, adding to the material, efficient, formal and final the causes they call "paradigmatic" and "instrumental."
The instrumental cause is relatively easy to see: a potter making two otherwise identical cups, using a kiln to fire the first but only the heat of the sun to bake the second produces to different cups, even though he has used the same clay and pattern to fashion them. The instrument used by the efficient cause, then, changes the resultant effect. In Aristotle's four causes we might include the instrumental as part of the efficient cause (because it acts as an extension of the efficient maker) or as part of the material cause (because it might be considered a part of the material with which the maker works) but it seems to be worth a category of its own.
The addition of the paradigmatic is, I think, more problematic: what is the difference between formal cause and paradigmatic? Let us return to the potter - what idea does he hold in his mind before he makes his cup? He must certianly hold a universal pattern of "cup" - that is to say, a shape which will provide an enclosed space for the containment of liquid. But he must also have a particular form in mind in order to produce his particular type of cup: this will include the particular capacity, shape, decoration, handle and so on, of his proposed cup. Thus what Aristotle calls essence and Donald calls form is revealed to be twofold, the universal and the particular, or what the later Platonists call paradigmatic (paradeigmatikon) and form (eidetikon).
Of the six causes, three are true causes (the final, paradigmatic and efficient) while the other three are accessories, being dependant upon the first three for their efficacy. See Lucas Siorvanes' book Proclus, Neoplatonic Philosophy and Science (Yale UP. 1996) for a fuller discussion of this fascinating development.
Yours John B
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