ay well be an incomplete picture of a certain situation,
but it is always a complete picture of something.) A probability
proposition is a sort of excerpt from other propositions.

5.2 The structures of propositions stand in internal relations to one
another.

5.21 In order to give prominence to these internal relations we can
adopt the following mode of expression: we can represent a proposition
as the result of an operation that produces it out of other propositions
(which are the bases of the operation).

5.22 An operation is the expression of a relation between the structures
of its result and of its bases.

5.23 The operation is what has to be done to the one proposition in
order to make the other out of it.

5.231 And that will, of course, depend on their formal properties, on
the internal similarity of their forms.

5.232 The internal relation by which a series is ordered is equivalent
to the operation that produces one term from another.

5.233 Operations cannot make their appearance before the point at which
one 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.

5.25 The occurrence of an operation does not characterize the sense of
a proposition. Indeed, no statement is made by an operation, but only by
its result, and this depends on the bases of the operation. (Operations
and functions must not be confused with each other.)

5.251 A fu