Full Idea
Three ways have been handed down in which people define the soul: what is most capable of moving things, since it moves itself; or a body which is the most fine-grained and least corporeal; or that it is composed of the elements.
Gist of Idea
Soul is seen as what moves, or what is least physical, or a combination of elements
Source
Aristotle (De Anima [c.329 BCE], 409b19)
Book Reference
Aristotle: 'De Anima (on the psuche)', ed/tr. Reeve, C.D.C. [Hackett 2017], p.16
A Reaction
A nice example of Aristotle beginning an investigation by idenfying the main explanations which have been 'handed down' from previous generations. These three aren't really in competition, and might all be true.