In Descartes philosophy Mind & Matter are two substances which he then found difficult explain how they affected each other.
This, on the face of it seems wrong. Conventionally, one supposes one has a mind, and that ones body is real; I think of moving my left foot one inch forward, and it does; empirically & observationally there appears no impediment between thought an action, between mind and body and thus matter.
Hence this cannot be Descartes starting point. Perhaps the key concept here is substance.
What is substance?
It is free of all accident, and is causally self-subsistent.
From this one deduces that mind and matter are substances. The question is are they the same substance. Where there is two, the possibility of reducing to one presents itself.
Now given that we have stipulated that a substance is causally self-subsistent, and given what we have observed above, mind moving matter, it seems that matter must be of the same substance as mind.
But there is another distinction that holds for substance, to remove all accident is to uncover the essence of a substance.
For mind differs in quality from matter in an essential way; mind has qualia, matter does not appear to do so. So these two substances are essentially different, yet they are causally active on each other. For if my mind is causally inert, then my mind, my stream of consciousness moves nothing - a quotation from Yeats is opposite here:
Our master Caesar is in the tent
Where the maps are spread,
His eyes fixed upon nothing,
A hand upon his head.
Like a long-legged fly upon the stream
His mind moves upon silence.
This is Descartes riddle.
If the distinction of qualia holds then one must explain causality between two differing substances.
If the observation of causality holds, then one must explain why qualia is not essential.
From 2, we can derive the doctrine of Idealism, all is mind; or that of physicalism, that all is matter.
From 1, we derive Spinozas system.
a. Is this a correct summary of Descartes position and how does he himself solve it?
b. Was Descarte the first to present this position, or was it well known in Medeival Theology?