None of the above, it would seem.

If it is the past year that we are commemorating, would we still drink to it if we were to receive some bad news about our health and imminent demise? Not likely. But why? What is the relevance of information about the future (our own looming death) when one is celebrating the past? The past is immutable. No future event can vitiate the fact that we have made it through another 12 months of struggle. Then why not celebrate this fact?

Because it is not the past that is foremost on our minds. Our birthdays are about the future, not about the past. We are celebrating having arrived so far because such successful resilience allows us to continue forward. We proclaim our potential to further enjoy the gifts of life. Birthdays are expressions of unbridled, blind faith in our own suspended mortality.

But, if this were true, surely as we grow older we have less and less cause to celebrate. What reason do octogenarians have to drink to another year if that gift is far from guaranteed? Life offers diminishing returns: the longer you are invested, the less likely you are to reap the dividenda of survival. Indeed, based on actuary tables, it becomes increasingly less rational to celebrate one's future the older one gets.

Thus, we are forced into the conclusion that birthdays are about self-delusionally defying death. Birthdays are about preserving the illusion of immortality. Birthdays are forms of acting out our magical thinking. By celebrating our existence, we bestow on ourselves protective charms against the meaninglessness and arbitrariness of a cold, impersonal, and often hostile universe.

And, more often than not, it works. Happy birthday!