5.233 An operation can first occur in the [a?] place where a proposition is generated from another in a logically meaningful [bedeutungsvolle] way. Thus in the place where the logical construction of the proposition begins.

So propositions are constructed? By us? Arbitrarily? Or by what rules?

Black (p. 260): “The idea is rather cryptically expressed. W. wishes simply to deny that there can be other than truth-functional operations.”