  For a broad range of cases, Aristotle implicitly makes twin claims about these four causes: (i) a complete explanation requires reference to all four; and (ii) once such reference is made, no further explanation is required. Thus, when appropriate, appeal to the four causes is both necessary and sufficient for completeness and adequacy in explanation. Although not all things which admit of explanation have all four causes, e.g., geometrical figures are not efficiently caused, even a brief overview of his psychological writings reveals that Aristotle regards all four causes as in play in the explanation of living beings. A monkey, for example, has matter, its body; form, its soul; an efficient cause, its parent; and a final cause, its function. Moreover, he holds that the form is the actuality of the body which is its matter: an indeterminate lump of bronze becomes a statue only when it realizes some particular statue-shape. So, Aristotle suggests, matter is potentially some F until it acquires an actualizing form, when it becomes actually F. Given his overarching explanatory schema, it is hardly surprising that Aristotle should advance a hylomorphic account of soul and body; this is, for him, standard explanatory procedure.