Context: Aquinas

The problem is something like this: for the parts of the human body to be 'one', they must have a form — this form is the principle of the body's unity. But if the soul itself has parts, doesn't this mean there should be a 'meta-soul' which unites the soul's parts?

Does Aquinas have anything to say about this? Am I misunderstanding something? Thanks!

  • It can not, the soul has no parts to unite, it is "simple". Blackerby helpfully collected relevant passages at the end of his thesis, p.237ff:"The Philosopher says in De Anima II, the soul is the form of the body. He also says there that the form is neither matter nor a composite. Therefore, the soul is not a composite", In Sent. 1 d.
    – Conifold
    May 3 '20 at 3:30
  • 2
    By "parts" do you really mean "powers of the soul"?
    – Geremia
    May 3 '20 at 3:48
  • Thank you both—yes, Geremia, I think I was thinking of powers of the soul, and Conifold, your references have given me confidence.
    – Cal
    May 3 '20 at 4:10
  • 1
    If there are parts, why wouldn't it be the soul itself which unites its parts, just as the body unites its parts? May 3 '20 at 6:07
  • Schroedinger finds even the idea of a multiplicity of souls absurd, uniting them in the world-soul in line with the early Classical Christian and Upanishadic teachings. So for him it is not the individual soul that needs to be unified but (our idea of) the multiplicity of part-less souls. .
    – user20253
    May 4 '20 at 14:59

By "parts", Aquinas clearly does not mean mereological parts; it is another term for "powers of the soul". The soul is no composite for him.

Therefore the question now becomes if he should have taken them to be mereological parts. IMHO, yes. Because the different powers of the soul relate to the body in very different ways. Isn't it quite inconceivable that the soul does not have parts but is both capable of operations in which matter is not involved and operations of a material nature?


There are may kinds of " wholes". When traditional ( aristotelian) philosophy said that the soul is a whole, it was understood as a " potential whole" the parts whereof are its powers ( cognitive power and appetitive powers being the " summa divisio").

In this sense, being a whole is not incompatible with being essentially one.

Link to " Medieval Mereology" https://plato.stanford.edu/entries/mereology-medieval/#PoteWhol

  • Doesn't Aristotle picture a tripartite soul?
    – CriglCragl
    Jun 2 '20 at 23:44

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