Obviously the hand is part of the body as a whole.
Equally obviously, it is not the same as the body
as a whole.
>Since formal language was derived from natural language, it is thus
>a part of it, and therefore a subset.
There are many formal languages. Whether any of them
derived from a natural language is probably debatable,
depending in large part on what you mean by "derived".
As this is not mathematics, the word "subset" is being
used metaphorically, and the use is therefore ill-defined.
One of the differences between natural and formal
languages is the possibility of metaphor and vague but
useful definitions, in natural language, which do not
occur in formal languages. Another is that the meanings
in natural languages are necessarily context-dependant.
But there obviously are similarities, even if only because
both types are languages. So the question becomes,
are they the same for the purposes (in the context) of
the present discussion? Now, I can't remember what
those purposes were. Can you?
Robin