Substance: In Aristotle and
ordinary language: What something is made of, as opposed to form, i.e.
any given shape(s) of the substance.
In the above terms, and
with Aristotle, we may distinguish between
the substance of a statue, such as bronze or stone, and the form of a
statue, such as its being shaped to look like Apollo or Socrates.
Note that while the distinction makes intuitive sense - as in "bread is
made of flour, milk, water and yeast, shaped into a loaf and baked in an
oven" - it is difficult to make precise in terms of logic or physics.
One fundamental difference tween
substances and forms that has been proposed is that the parts of
substances - such as a bit of bronze, a piece of a loaf of bread - has
the same defining properties as what is part of, while this holds not
for things that are forms.