In his treatment on hope, one of the first aspects Aquinas clarifies is that despite what it looks like hope is a theological virtue and a habit that has a future good in God. He writes: “[W]hen we were treating of the passion of hope, the object of hope is a future good, difficult but possible to obtain.” Thus, for Aquinas “the object of hope is the eternal happiness.” (II-II, Q.17, A.2). From here one concludes that Aquinas’s notion of hope seems to have a theological character because it attains to God himself who helps us to obtain such happiness. In this sense as well, Aquinas defines hope as a “movement… [of the will] towards an arduous good.” (II-II, Q.17, A.3). In his Article 5 of Question 17, Aquinas asserts that hope is indeed a theological virtue since God is the main object of this habit.
Related to hope it is the discussion of despair. For Aquinas, despair is the opposite movement of hope. While hope moves towards a good, despair moves to the “conformity with false opinion about God.” (II-II, Q.20, A.1). This makes despair to be considered both vicious and sinful. And because despair is a sin, then, it is an aversion of the good. Aquinas writes, “In every mortal sin there is, in some way, aversion from the immutable good” (II-II, Q.20, Reply Obj 1). But the rejection of the immutable good is not the only thing despair does. Despair also transforms such good into a mutable good turning a person’s soul into those mutable goods. In that regard, for Aquinas despair is a theological vice because it departs people from God and His goodness (Cf. II-II, Q20, Reply Obj 1).
Importantly, Aquinas understands that despair is both a sin itself and the source of other sins (q20, a1). By this, he means that after a person enters into a state of despair, he or she gives up to other sins or vices such as lasciviousness or covetousness. Since despair turns a person into a false belief about God, it is not strange that such situation leads a person to believe false statements about other sinful actions as well. That is, despair is both an aversion and conversion: an aversion of the good and a conversion to a false good. (II-II, Q.20, A.1, Reply to Obj 1). In this way, a person in despair not only rejects the true good but embraces a false one.
Unlike despair, presumption is an “immoderate hope” that instead of depending on God to obtain the good, it depends on a person’s strength (II-II, Q.21, A.1). That is, when a person relies on his or her own strength instead of God’s, he or she is rejecting God. Therefore, presumption is also a sin. But dissimilar to despair, Aquinas considers it is “less grave” (II-II, Q.21, A.1). Noteworthy to mention is that presumption and despair are two opposite vices, but both oppose to hope (II-II, Q.21, A.3).