One area in which Galen openly asserts his ignorance is that of the “substance/essence (ousia) of the soul”: is it a non-bodily substance, as Plato thought, or composed of physical elements? (See further §6.4 on ousia and 7 on soul-theory.) In spite of some strong apparently physicalist statements in this area, Galen consistently throughout the corpus denies that he knows the answer to this question (Donini 2008; Singer 2013: 32–33 and Ch. 4). The case is similar in response to the question, how information is transmitted into the embryo in the process of conception and foetal development. That one needs to invoke some form of “intelligent design” is, to Galen, absolutely clear. But precisely who or what is responsible? How does the infant acquire, from birth or even before, the ability to perform all its innate functions? In an interestingly open-ended discussion in The Shaping of the Embryo (Foet. Form. 6, 196–201), Galen ends with a genuine aporia: all existing options within the tradition—the Platonic “world soul” extending throughout matter, the presence of a rational soul in a pre-rational animal, a plurality of souls for each individual muscle function—have consequences which make them unattractive; but he does not himself claim to have the answer.