I mean here to treat briefly, if haphazardly, of some gleanings from Aquinas’ considerations of faith; especially faith as propositional. John Bishop, via the Stanford Encyclopedia (http://plato.stanford.edu/entries/faith/), informs that interpreting the famous Dominican is difficult as ‘faith’ is primarily used to describe a mental state (I agree with…) while St. Thomas uses the term to mean the way a believer is related to God. Taken in this sense, belief is not primarily propositional. Perhaps, as Bishop suggests, belief in does not perfectly align with belief that.
This is not to suggest that Aquinas is unconcerned with propositional aspect of faith. Rather, there is room to consider the will and ration in a Thomistic model. He then describes faith, in the Second Article, Part II from Summa, as ‘a mean between science and opinion’, both of which concern propositions, but the act of believing them concerns less their propositional value than their origination in God and their leading towards Him (as Terence Penulham via Bishop). Faith is then based not primarily on content, but rather on divine testimony (akin in my mind to the role of prophecy for Ghazali – perhaps worth scaring up as Aquinas ought at least to have been familiar with an Avicennan model of prophecy).
Further, as noted in Objection 2, faith is explained by way of symbol. This is exceptionally strange if the content of the faith-object is purely propositional but unsurprising when we note that the action of the believer ends in a thing, not a proposition. I.e. I think, my faith act is incomplete if it stops at agreement; Christ called followers to actively align their footsteps (and far more) with His. Faith is not purely rational; and neither is truth. Aye, it is propositionally understood, but it is also understood symbolically – both by analogy and combining of similar thoughts. There is space for metaphor so long as our object is right action. “For as in science we do not form propositions, except in order to have knowledge about things through their means, except in order to have knowledge about things through their means, so is it in faith. (Reply Obj. 2)”
So then, faith can be understood propositionally — but not solely. The primary expression of faith is submitting the will. Which then is better, faith as typically understood or faithfulness? One certainly costs more of the seeker — perhaps everything.