Quote:
Originally Posted by Cheshire Cat  Substance doesn't have to be material. Take for example the substance of the self in Cartesian substance dualism. |
I would argue that the implies something physical, at least in common usage (now at least). However, it looks like it can also be used metaphorically, i.e. when speaking of the "substance" of a conversation, or also when speaking of philosophy, as you and the Catechism have shown.
I prefer "essence" (Latin
esse, "to be") and "nature."