Full Idea
To create the soul the god combined two kinds of substance - one indivisible and never changing, the other the divided and created substance of the physical world - with intermediates between them, and then a homogeneous mixture.
Gist of Idea
The soul is a complex mixture of pure mind and changing matter
Source
Plato (Timaeus [c.362 BCE], 35a)
Book Reference
Plato: 'Timaeus and Critias', ed/tr. Waterfield,Robin [OUP 2008], p.23
A Reaction
Interestingly, this does not imply simple mind-matter dualism, but includes bridging intermediates, ending in what seems to be a continuum between physical and mental. Not to be taken too seriously, though. Plato admits it is all speculation.