We shall say that the
rule is
involved in the understanding, obeying,
etc., if, as I should like to express it, the symbol
of the rule form
s part of the calculation.
(As we are not interested in where the processes of thinking,
calculating, take place, we can, for our purposes, imagine the
calculations being done entirely on paper. We are not
concerned with the difference: internal,
external.)
21.