Thomas Aquinas, in the Summa Theologiae II-II, Question 2, addresses the question of faith. From the first article we can see that he follows in the footsteps of St. Augustine. The question that is addressed in the first article is “Whether to Believe is to Think with Assent?” After considering 3 objections to the contrary, Aquinas answers, “On the contrary, This is how to believe is defined by Augustine.” Aquinas goes on to elaborate Augustine’s definition by distinguishing between, three senses in which we use the word think. The first sense is the general sense and seems to imply, for Aquinas, knowledge, that is, the end of the thinking process. This sense is what is behind the affirmation “I think X.” X is a conclusion, an object of knowledge. Aquinas claims that if faith is to think with assent in this first sense, then even those objects of knowledge which have been gained through science must be said to be the objects of faith, which is ridiculous. Aquinas says, “If to think be understood broadly according to the first sense, then to think with assent, does not express completely what is meant by to believe: since, in this way, a man thinks with assent even when he considers what he knows by science, or understands.” The third sense that Aquinas gives is the definition of the term, that is, “an act of the cogitative power.” This third sense is too general because it includes both the first and the second sense; therefore it cannot be the third sense of to think.
Logically, if there are only three options, and the first and the third are not the proper ways of understanding to think, then the second sense of to think must be the correct sense. Leaving the question of whether or not there are only three senses of to think to another time, we will look at Aquinas’s explanation of the second sense. Aquinas says that the second sense of to think refers to the actual process, or act, of thinking prior to the arrival at a conclusion. “In this way thought is, properly speaking, the movement of the mind while yet deliberating, and not yet perfected by the clear sight of truth.” So, to think, in the second sense, is an unfinished process by which the thinker tends towards, though they have not yet arrived at, the truth. In this way alone, can we understand Augustine’s definition of to believe. To believe is not to possess the truth, and it is not, therefore, knowledge. Yet, to believe implies a conviction of the truth of the object of belief which is equal to the conviction of the truth of an object of knowledge. In other words, the believer is as convinced of the truth of the object of belief as the knower is of the object of knowledge (which is necessarily true). Aquinas says, “But this act to believe, cleaves firmly to ones side [is firmly convinced of the truth of one side of an argument, for example that God is triune], in which respect belief has something in common with science and understanding [because science and understanding also cleave firmly to one side of the argument due to the knowledge of the truth of that side and the falsity of the opposite opinion, for example that it is true that “Australia is a continent in the southern hemisphere.”]; yet its knowledge does not attain the perfection of clear sight, wherein it agrees with doubt, suspicion and opinion.”
Belief, therefore, is like knowledge in its conviction of the truth of the proposition, but it is like, as Aquinas states, doubt, suspicion and opinion in the sense that the proposition is not the object of knowledge for the person in question, or, in other words, the proposition is not seen to be true by the person in question. Therefore, belief is accepting voluntarily the truth of a proposition (that is not, or cannot, be seen to be true by the believer) based upon the authority of an intellect which offers the proposition for belief, and which has sees the truth of the proposition.