proposition is generated out of another in a logically meaningful way; i.e.
the point at which the logical construction of propositions begins.


5.234 Truth-functions of elementary propositions are results of operations
with elementary propositions as bases. (These operations I call truth-
operations.)


5.2341 The sense of a truth-function of p is a function of the sense of p.
Negation, logical addition, logical multiplication, etc. etc. are
operations. (Negation reverses the sense of a proposition.)


5.24 An operation manifests itself in a variable; it shows how we can get
from one form of proposition to another. It gives expression to the
difference between the forms. (And what the bases of an operation and its
result have in common is just the bases themselves.)


5.241 An operation is not the mark of a form, but only of a difference
between forms.


5.242 The operation that produces 'q' from 'p' also produces 'r' from 'q',
and so on. There is only one way of expressing this: 'p', 'q', 'r', etc.
have to be variables that give expression in a general way to certain
formal relations.