  Aristotle claims that in a chain of efficient causes, where the first element of the series acts through the intermediary of the other items, it is the first member in the causal chain, rather than the intermediaries, which is the moving cause (Physics 8.5, 257a10–12).  Then, both in cases of natural generation and artificial production, it is only this first efficient cause which has to satisfy the requirement of synonymous causation.  Aristotle’s prime example, that human  generates human, is also such a case. Here, the causal efficacy of the  paternal human form is transmitted through the generative  potentialities of the semen of the father. The semen, however, although  it acts as an efficient cause in the process of the formation of the  embryo, is not a human; it does not possess the form it transmits in  the same way as the male parent. Aristotle’s  discussion makes it clear that this is not an isolated instance of an exception from the general principle.  He compares the case to the activity of a craftsman, where the form of the product of the artistic production is in the soul of the craftsman, and then through the motions of the instruments this form can get imposed on the material manufactured into an artefact. The instruments and their motions are efficient causes of the process, but they do not contain the form in the same way as the soul of the craftsman (On the generation of animals 730b14–23 and 740b25–29, for further discussion see the entry on  Aristotle’s biology).[30]