Lastly, the sperm of the male acts like a cunning workman who makes a work of art, using heat and cold as the workman uses his tools: for this heat and this cold could never of themselves--by coagulations and condensations--produce the form of the body as the older naturalists had supposed, regarding only the efficient and ignoring the formal and the final cause: for the organic body is not what it is because it is produced in such and such a fashion, rather it is because it is to be such and such that it must be developed as it is. And here lies the kernel of the whole matter. For while Aristotle has made it perfectly plain that, according to his idea, the soul, at least its nutritive and perceptive faculties, is to be regarded as a function of matter and that this function may be ultimately expressed in terms of movement, and further that development is a mechanism which is set going by the communication of motion proceeding from the ‘soul’ of the male element and derivable eventually from the motions into which the ‘functions’ or ‘soul’ of the parent can be resolved to the mere matter which the female provides, it is equally evident that he does not regard this mechanical explanation--in terms of material and efficient causes--as satisfactory or complete. But when we inquire why, he gives us no certain nor consistent answer. On the one hand, there are passages in which he tells us that there must be something which controls the material forces and imposes on them a limit and proportionality of growth; that the soul makes use of them as the artist makes use of his implements, and such passages are naturally interpreted by Driesch in the sense of a ‘dynamic’ teleology; it is the ψυχή which superintends and controls, and the ψυχή is ‘entelechy’. Elsewhere, however, we are informed that even the proportionality of the developing parts is simply the outcome of the motion imparted by the male, which is _actu_ what the female element only is _potentia_. Moreover, it may be questioned whether Aristotle ever intended to imply more than an ‘analogy with the causality of purpose’ when he uses the figure of the workman and his implements to illustrate his meaning of the formal cause. The formal cause of a work of art is an intelligible _vera causa_; it is the idea in the mind of the artist antecedent to the execution of the work; but the formal or final cause of an organism, the end which it apparently strives to attain, can only be said by a metaphor to be prior in time to the existence of the organism itself. Prior in thought, however, it certainly is, for it is only the performance of its functions (ἐντελέχεια) by the organism complete in all its parts that makes the mere mechanism of development comprehensible to us; the process, therefore, exists for the sake of the end. Only as efficient cause is the soul prior in time; only so far as it is prior in thought can it be said to be a final cause.