Now, in the object of hope, we may note four conditions. First, that it is something good; since, properly speaking, hope regards only the good; in this respect, hope differs from fear, which regards evil. Secondly, that it is future; for hope does not regard that which is present and already possessed: in this respect, hope differs from joy which regards a present good. Thirdly, that it must be something arduous and difficult to obtain, for we do not speak of any one hoping for trifles, which are in oneâ€™s power to have at any time: in this respect, hope differs from desire or cupidity, which regards the future good absolutely . . . Fourthly, that this difficult thing is something possible to obtain: for one does not hope for that which one cannot get at all: and, in this respect, hope differs from despair.
Thomas Aquinas, Summa Theologica, Benziger Bros./Accordance electronic ed. (Altamonte Springs: OakTree Software, 2004), Iâ€“II.40.1.