 Needless to say, not all why-questions are requests for an explanation that identifies a cause, let alone a cause in the particular sense envisioned by Aristotle. Still, Aristotle is clearly committed to the view that giving the relevant cause (or causes) is necessary and sufficient for offering a scientific explanation. His conception of a cause has both a metaphysical and an epistemological  component. Part of the challenge for us is to do justice to both components. Following a recent suggestion, we may say that “causes are not ways in which we explain things, except derivatively, in virtue of the fact that they are ways in which some elements of the natural world explain others” (Stein 2012a: 705).