 Diogenes Laertius, in his Lives of the Philosophers (3rd century AD), includes Alcmaeon among the Pythagoreans and says that he studied with Pythagoras (VIII. 83). Later authors such as Iamblichus (VP 104, 267), Philoponus (De An. p. 88), and the scholiast on Plato (Alc. 121e) also call Alcmaeon a Pythagorean. A majority of scholars up to the middle of the twentieth century followed this tradition. However, it is not true that the ancient “tradition is unanimous in presenting him as a Pythagorean” (Zhmud 2012a, 123). In fact, the majority of ancient sources do not describe him as a Pythagorean (e.g., Clement [DK 24A2], Galen [DK24A2], Aetius [DK 24A4, 6, 8–10, 13, 17–18], Censorinus [DK 24A13–14], and Chalcidius [DK A10]). The best argument for regarding him as Pythagorean would be his inclusion in Iamblichus’ catalogue of Pythagoreans at the end of his On the Pythagorean Life, if we could be sure that all parts of that catalogue go back to Aristoxenus in the fourth century, since Aristoxenus is a very knowledgeable source on Pythagoreanism (Zhmud 2012a, 122; 2012b, 241–43). However, certain parts of the catalogue are very unlikely go back to Aristoxenus and we cannot be certain that the inclusion of Alcmaeon was due to him (Huffman 2005, 297–99). Apart from this possibility regarding Aristoxenus, no one earlier than Diogenes Laertius (ca. 200 AD) calls Alcmaeon a Pythagorean. Aristotle wrote two books on the Pythagoreans but wrote a separate book on Alcmaeon. Aristotle and Theophrastus refer to him a number of times but never identify him as a Pythagorean, and this is the practice of the doxographical tradition (see A4, 6, 8–10, 13–14, 17–18, in DK 24). Simplicius (6th AD) reports that some have handed down the view that Alcmaeon is a Pythagorean but notes that Aristotle denies it (De An. 32.3). Most telling is Aristotle’s discussion of Alcmaeon in Metaphysics book I (986a22 ff.). He notes a similarity between Alcmaeon and a group of Pythagoreans in positing opposites as the principles of things but expresses uncertainty as to who influenced whom. Earlier scholars took this comparison of Alcmaeon to the Pythagoreans as confirmation that he was a Pythagorean. Most scholars of the last fifty years, however, have come to recognize that Aristotle’s treatment of Alcmaeon here suggests the exact opposite; it only makes sense to compare him with the Pythagoreans and wonder who influenced whom, if he is not a Pythagorean (e.g., Guthrie 1962, 341: “Aristotle … expressly distinguishes him from the Pythagoreans”). Certainly most of the opposites which are mentioned as crucial to Alcmaeon do not appear in the Pythagorean table of opposites, and there is no trace of the crucial Pythagorean opposition between limit and unlimited in Alcmaeon. The overwhelming majority of scholars since 1950 have accordingly regarded Alcmaeon as a figure independent of the Pythagoreans (e.g., Guthrie 1962, 341; Burkert 1972, 289; KRS 1983, 339; Lloyd 1991, 167; Kahn 2001; Riedweg 2005, 115; Primavesi 2012, 447. Zhmud [2012a, 121–124; 2014, 97–102] is the notable exception), although, as a fellow citizen of Croton, he will have been familiar with their thought.