 Macrobius (5th century AD) is the only ancient source to attribute to Philolaus the doctrine that the soul is a harmony (DK 44 A23). It is not clear that this ascription is based on anything in Philolaus’ book, moreover, and it may just be a conclusion based on the espousal of the doctrine by Simmias, who is presented as a pupil of Philolaus, in Plato’s Phaedo (86b5 ff.). The doctrine as presented in the Phaedo may be Plato’s invention based on several Presocratic sources (Mansfeld 2010b: 183–188). However, since Philolaus believed that all things were either limiters, unlimiteds or harmonious combinations of limiters and unlimiteds, it is not implausible that he would have regarded soul as such a harmony of limiter and unlimited. In Fr. 13 soul (psychê) is the center of emotions and desires, is associated with sense perception, and has its seat in the heart (see 5.1 above). Sedley argues that Philolaus’ embryology (see 6.1 below) suggests that a body is first ensouled when the heat (an unlimited) of the embryo was cooled, and hence limited, by breath. The soul can thus be viewed as a harmony of these and other opposites, which is the view that Simmias presents in the Phaedo (Sedley 1995, 22–6). In the Phaedo, however, the view that the soul is a harmony of parts of the body is shown to be in conflict with its immortality. Some have thus thought that Philolaus did not believe in the immortality of the soul or transmigration (see now McKirahan 2016). It is more likely, however, that he regarded the psychê, which was the center of desires and emotions located in the heart and shared with animals, as a harmony of its own material elements. This may have been drawn in with the first breath of the infant and from its seat in the heart it may have served as the command center which establishes the harmony of hot and cold which makes the body ensouled. After the body loses its harmony and dies, this command center soul survives to transmigrate into the hearts of other animals and men. If the psychê was the transmigrating soul for Philolaus, it follows that he did not think that humans were reborn as plants, since according to Fr. 13 plants do not have a psychê. Moreover, it would only be the human character as constituted by emotions and desires that transmigrates and not human intellect, since according to Fr. 13 psychê does not include intellect (Huffman 2009; for a critique see Palmer 2018).