According to King, Jubien's objections to the existence of propositions somewhat do not apply to his version of what propositions are. King says that Jubien classifies his theory of propositions as an ontological account (as opposed to a mathematical variety). Jubien's definition of an ontological account is something that explains propositions as platonic in nature and having constituent parts (properties). King's propositional theory states that propositions actually are dependent on conscious entities and would not have existed without them. King's account of Jubien's 1st objection can be written as follows:
1) Propositions represent or have truth conditions as a result of their "internal make up".
2) Because of (1), the representational capacity of propositions must be grounded in the representational capacity of its constituents.
3) The representational capacity of the constituents of propositions must be grounded in the nature of the constituents themselves.
4) The nature of the constituents of propositions are unique mereological fusions or sums of properties and relations.
5) But mereological sums of properties and relations do not give way to unique propositions
6) Anything that is both necessarily unique and not unique at the same time cannot exist
7) Propositions must not exist
King responds by addressing the validity of the first Premise. The reason Jubien takes (1) to be the case is that if it were the case that propositions could represent or have truth conditions as a result of external causes, then something else could have been the proposition in question. If two things have the same claim to something then, according to Jubien, they fall prey to the Benacerraf dilemma and neither can say they are the real proposition (instead they are merely surrogates or models of it). In notational form this can be as follows:
i) An external cause that gave truth conditions to a proposition could have given it to other propositions.
ii) All propositions with the same truth conditions have an equal claim to being the true proposition.
iii) If more than one proposition can claim to be the true proposition then they fall prey to the Benacerraf dilemma
iv) Externally caused propositions fall prey to the Benacerraf dilemma.
At this point, King questions premise (i); whether Jubien means a) something actually has an equal claim to the proposition in question, or b) something could have an equal claim to the proposition in question.
In the case of (a), King outright rejects it as false. King states that "the facts I claim are propositions are intrinsically the most eligible facts for that role".
In the case of (b), King rejects this because only things that "actually are" can cause a Benacerraf dilemma.
By showing that premise (1) does not apply to his theory of propositions, King has in effect shielded his theory from all subsequent consequences of that premise, namely all of Jubien's arguments against propositions (kind of chopped the legs off of him).
It seems to me that King had already pointed out that his theory of propositions does not fall under the category of those objected to by Jubien. I would have been very surprised if, having already stated that, he ran into trouble defending his theory. I think at one point he even says that he will defend his theory from Jubien's objections for the "intrinsic interest of his arguments".
The only problem that I have is that I didn't quite catch where King does attribute his proposition's truth conditions from (an external source I imagine seeing how he is not a fan of the internal view). All I know is that according to him it could be an external source without having to worry about the Benacerraf dilemma.