 Any theory that construes propositions as structured entities would seem to face the problem of the unity of the proposition.  It is not entirely straightforward to say what this problem or set of problems is.  But at the very least, there are at least two problems here.  There is the problem of explaining why one sort of structured whole, a proposition, can be true or false, while the set of its constituents is not.  A list isn’t true or false, and a proposition with the same constituents is; why is this?  Second, there is a general problem of explaining how two distinct things could have all the same constituents.  For a thorough discussion of the history of philosophical work on the unity of the sentence and the proposition, the reader should consult Gaskin (2008).