In the general propositional form, propositions occur in a proposition only as bases of the truth-operations.
5.541 At first sight it appears as if there were also a different way in which one proposition could occur in another.
Especially in certain propositional forms of psychology, like "A thinks, that p is the case", or "A thinks p", etc.
Here it appears superficially as if the proposition p stood to the object A in a kind of relation.
(And in modern epistemology (Russell, Moore, etc.) those propositions have been conceived in this way.)
5.542 (3) But it is clear that "A believes that p", "A thinks p", "A says p", are of the form "`p' says p": and here we have no co-ordination of a fact and an object, but a co-ordination of facts by means of a co-ordination of their objects.