I answer that, The species of a passion is taken from the object. 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 one's power to have at any time: in this respect, hope differs from desire or cupidity, which regards the future good absolutely: wherefore it belongs to the concupiscible, while hope belongs to the irascible faculty. 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. It is therefore evident that hope differs from desire, as the irascible passions differ from the concupiscible. For this reason, moreover, hope presupposes desire: just as all irascible passions presuppose the passions of the concupiscible faculty, as stated above (Question [25], Article [1]).