This argument is an elaboration on something presented in Part 4 of my Dialogue on Philosophy and Ethics. My argument is very simple and relies on premises that are obscured more than weird. The structure is like this:
1) Everything that acts, acts for an end that it could possibly achieve
2) Man acts for perfect happiness
3) Perfect happiness is that state of affairs in which man could find no reason to act further
4) As long as there is impermanence, man will find reason to act
5) Therefore, man must be able to reach a permanent (immortal) state of affairs
I will reckon that the most difficult premise to argue will be that everything which acts, acts for an end that it may possibly achieve. I am also certain that there will be some confusion on the point of what constitutes perfect happiness for man, but I believe that is more a matter of confusion and, following my elucidation, it will be cleared up.
The idea of finality, or final cause, variously referred to as a thing’s end, aim, or directed-ness, is given an embarrassing amount of short shrift by those who ought to know. Its understanding and, resultantly, acceptance is largely what separates modernist philosophers from those of a more Scholastic, Thomistic bent. Modernists try and maintain that finality was done away with by the advent of natural science, but that this is not the case is quite clear from an examination of the concepts maintained even by our supposedly “undirected” sciences. Though admittedly, perhaps some of the blame may be laid with Aristotle, who is typically called upon to explain the idea, for which he explains it rather poorly. Still, that is no excuse for being wholly ignorant of the clarity brought to the concept by 2000 years’ worth of philosophers who followed him.
Finality is the idea that a thing is acting, or moves itself, to the attainment of a state in which it would achieve its aim, coming to rest and thus having no further reason to act. This may sound strange to those unacquainted, but it can be demonstrated that we all implicitly rely on there being just such a thing when we attempt to explain the action of a thing. I will present some examples in order that the concept be made clear in our own explanations, whether they are “everyday” or “scientific.” I wish to note in these explanations that, when we state why something does what it does, it is in order to achieve some end. Note our use of descriptions such as “in order that,” “directed to,” “to attain,” and so on.
Gravitation is a very basic example. A stone falls in order that it may lie on the ground. Whenever we see a stone, and see that it is falling, we suppose it is the case that there is some ground to which it is falling. Gravity is always and everywhere an attraction of material bodies to each other.
Gases also behave with directed-ness. One example is their behavior to maintain an inverse proportion between pressure and volume.
Finality is present in living things as well. A seed has as its end to grow into a mature adult.
And every animal has as its end to maintain and generate more life.
In fact, these ends are so essential that we explain the parts of a whole living being in terms of how they help it to achieve its end. Not only can we not explain a thing without reference to its final cause, but this final cause is so important that it is the principle by which we recognize that a thing is what it is. An animal has teeth in order that it may gain nutrition to gain energy in order that it may continue living. And while I don’t have any knowledge about seeds, I reckon that its parts are explained in terms of how they help that seed to achieve its end.
If you have any lingering doubts about the necessity of finality in explaining a thing, then I can present this challenge. Try and produce, to your own satisfaction, an explanation of gravity that does not even implicitly rely on the fact that a thing falls in order to reside at a lowest point. I will note that my argument is not that a thing will necessary achieve its end; an animal may die before procreating or starve, a sapling may be drowned, a stone might burn up in a planet’s atmosphere, and so on. However, in every case there is the possibility that a thing will achieve its end. A seed may not actually become a mature adult, but there is in respect to the reality of the world that possibility, and this no matter how unlikely for its present environment (say, a seed that tries to grow on the moon; it is only that there is, for all things considered, the possibility that it could achieve its end somehow). Though, when a thing attains this end and has no further reason to impel itself beyond, say when a stone finds the ground and so rests there by inaction, we can say that a thing has perfected its end. A thing brought to perfection is a thing without further reason to act, at least until it is the case that it is moved from its place of finality (like, when I pick up the stone and throw it in the air), whereupon it will act again to be brought back to its place of rest.
Now I argue this. Seeing as everything in the world has some end to which it acts, then we can only suppose that humans likewise have something to which they act, and this is what distinguishes humans in their essence from everything else. Arguing that, yes, everything else has an end which it might possibly achieve but holding a reservation as to the possibility of humans achieving their end is special pleading. It is much simpler to suppose that, in the case that everything else acts to an end it has the possibility of achieving, humans also have this same possibility in respect of their own end.
Which brings about the question of what man’s end is. For what do we act?
I propose that we act in order to be happy. We note that whenever someone does something, they are trying to achieve some specific end, and this because they judge it to be more preferable to other acknowledged acts. A person works in order to generate an income that they might buy the things they like, or they get up from the couch to walk to the kitchen and get a drink of water. In all these things, a person expends labor in order to achieve some more preferable state. In general, a person acts in order to be happy, whether they would find some intermediate happiness in a fine meal or the company of a friend.
However, there is a defect of this world in that it can not bring a person to perfect happiness. For every intermediate end achieved, a person is left unsatisfied. This is proved in that a person must act further no matter how desirable we might judge their state of affairs. I reckon that even a person living in Eden should be left unsatisfied outside the achievement of perfect happiness. A great quantity of happiness is still not perfect happiness, a state of affairs in which a person finds no reason to act further. And what impels us to act further? This is because everything in this world is impermanent, and so it passes away in its consumption. Food is eaten, and so in being enjoyed it can be no longer enjoyed (in fact, eating will eventually make eating not enjoyable). Rest is the consumption of time for enjoying comfort, but in so being consumed it passes away.
Therefore, I find that this world cannot of itself bring us to our end.
But remember that everything has the possibility of reaching its end! If man cannot reach his end in this world, then it must be a defect of the world rather than a defect in man. This world simply cannot supply man his perfection or completion. It is just not the right kind of place, much like empty space is not the right kind of place for a stone, for we see that it continues to move until it lays on the ground. The relevant defect that makes it impossible for man to achieve his end in this world is its essential impermanence. Nothing can remain the same, but is always changing, and this in order that it may be as it is (for otherwise it would not be; a body at absolute zero would have zero energy and would consequently have no mass, making it cease to be).
If impermanence in this world is the defect that prevents man from reaching his end, then it must be possible for man to reach a state of permanence, which is outside of this world. If this is the case, then what binds man to this world, his remaining impermanent, must be negatable, and so an individual must be able to be forever, and this not merely to say that he might potentially continue living in this world without ceasing, as it is not this world that can bring man his happiness. That is, we could note that even a person who lives forever in this impermanent world would never achieve his end, and so the possibility would not be realizable. Therefore, the possibility of man’s happiness must lie beyond this world, while man must be able to live beyond the impermanence of this world in some way.
A man who can live in permanence is, we should note, what we mean by saying that he is immortal.