All this comes to saying that the person of whom we say
“he has pain” is, by the rules of the game, the
person who cries, contorts his face, etc..
The place of the pain ‒ ‒ ‒ as we have said ‒ ‒ ‒ may be in
another person's body. If, in saying
“I”, I point to my own body, I model the use of
the word “I” on that of the demonstrative
“this person” or “he”.
(This way of making the two expressions similar is somewhat
analogous to that which one sometimes adopts in mathematics, say in
the proof that the sum of the three angles of a triangle is
180˚.
We say
“α =
α'”,
“β =
β'”, and
“
γ =
γ”. The first two
equalities are of an entirely
115.
different kind from the
third.) In “I have pain”,
“I” is not a demonstrative pronoun.