 Aristotle refers to the Pythagoreans frequently in his extant works, especially in the Metaphysics. There are several puzzles about these references. First, his usual practice is to refer to the Pythagoreans as a group rather than naming individuals. He mentions Philolaus and Eurytus by name only once each and Archytas four times. Yet, the basic Pythagorean system which he describes in most detail in Metaphysics 1.5 shows such strong similarities to the fragments of Philolaus that Philolaus must be the primary source (Huffman 1993, 28–94, Schofield 2012, 147), although some scholars emphasize that Aristotle clearly did use other sources (Primavesi 2012, 255) and even that Philolaus, while perhaps the acme of Pythagorean philosophy, might not have represented mainstream Pythagoreanism thus explaining why Aristotle refers to the Pythagoreans as a group rather than singling out Philolaus (McKirahan 2013). Second, he frequently refers to the Pythagoreans that he discusses as the “so-called” Pythagoreans. Why does he add the qualifying phrase “so-called?” This phrase indicates not that these are false Pythagoreans in contrast to some other true Pythagoreans but rather that this is the standard way of referring to these people, it is what people call them; but the phrase also indicates that Aristotle has reservations about the name. Aristotle is expressing his doubts about how or whether these figures are connected to Pythagoras himself, whom Aristotle regards as a wonder-working founder of a way of life rather than as participating in the tradition of Presocratic cosmology (Huffman 1993, 31–34). It could also be that it is the very variety of sources that Aristotle is using that leads him to recognize that there are quite different stages in the develpment of Pythagoreanism and hence to wonder in what sense a figure like Philolaus who is at the end of that development should still be called a Pythagorean (Primavesi 2014).