The argument from desire is an argument for the existence of the immortality of the soul. The best-known defender of the argument is the Christian writer C. S. Lewis. Briefly and roughly, the argument states that humans' natural desire for eternal happiness must be capable of satisfaction, because all natural desires are capable of satisfaction. Versions of the argument have been offered since the Middle Ages, and the argument continues to have defenders today, such as Peter Kreeft and Francis Collins.

Versions of the argument from desire were commonplace during the Middle Ages and Renaissance. Here is one way Aquinas states the argument:

"It is impossible for natural desire to be empty, for nature does nothing in vain. Now, a natural desire would be in vain if it could never be fulfilled. Therefore, man's natural desire [for a final happiness proper to his nature] is capable of fulfillment. But not in this life, as was shown. Therefore it is necessary that it be fulfilled after this life. Therefore, man's ultimate felicity is after this life."

In this form, the argument depends crucially on the Aristotelian dictum that "nature does nothing in vain". Medieval critics of the argument, such as Duns Scotus, questioned whether the dictum is strictly true. Scotus pointed out that many animals seem to have an instinct for self-preservation.

But Aquinas's argument is also crucially based on the premise that "in things with cognition, desire follows cognition," and since animals have no intellectual cognition, i.e., no properly conceptual cognition, they have no concepts of eternal life or final happiness and thus are wholly incapable of desiring such things. A fortiori they cannot be said to have a natural desire for them.

The most prominent recent defender of the argument from desire is the well-known Christian apologist C. S. Lewis (1898–1963). Lewis offers slightly different forms of the argument in works such as Mere Christianity (1952), The Pilgrim's Regress (1933; 3rd ed., 1943), Surprised by Joy (1955), and "The Weight of Glory" (1940). Unlike medieval versions of the argument from desire, Lewis does not appeal to a universal, ever-present longing for eternal happiness but to a specific type of ardent and fleeting spiritual longing that he calls "Joy."

Lewis uses the term "Joy" in a special sense to refer to a particular type of desire, longing, or emotional response that he assumes will be familiar to at least most of his readers. Joy is a form of desire, Lewis claims, but of a unique sort. Experiences of Joy are brief, intense, thrilling "pangs" or "stabs" of longing that are at once both intensely desirable and achingly painful. Though Joy is a form of desire, it differs from all other desires in two respects. First, whereas other desires "are felt as pleasures only if satisfaction is expected in the near future," with Joy "the mere wanting is felt to be somehow a delight." Joy thus "cuts across our ordinary distinctions between wanting and having. To have it is, by definition, a want: to want it, we find, is to have it".

Second, Joy differs from all other desires in the mysteriousness or elusiveness of its object(s). With Joy, it is not clear exactly what is desired, and false leads are common. Many suppose, wrongly, that Joy is a desire for some particular worldly satisfaction (sex, aesthetic experience, etc.). But all such satisfactions, Lewis argues, turn out to be "false Florimels," delusive images of wax that melt before one's eyes and invariably fail to provide the satisfaction they appear to promise. It is this second unique feature of Joy—the fact that it is a strangely indefinite desire that apparently cannot be satisfied by any natural happiness attainable in this world—that provides the linchpin for Lewis's argument from desire.