The operation is that which must happen to a proposition in order to make another out of it.
5.231 And that will naturally depend on their formal properties, on the internal similarity of their forms.
5.232 The internal relation which orders a series is equivalent to the operation by which one term arises from another.
5.233 The first place in which an operation can occur is where a proposition arises from another in a logically significant way; i.e. where the logical construction of the proposition begins.
5.234 (1) The truth-functions of elementary proposition. are results of operations which have the elementary propositions as bases. (I call these operations, truth-operations.)