I would like to adopt and institute the practice of writing a Christmas reflection.  Some years, it might be a story.  At any rate, it seems appropriate for one who likes to write, just as many people enjoy baking especially for the holidays. Philosophers nowadays will sometimes frame an argument in terms of “possible worlds.”  One reason for this is because it helps distinguish between what is logically possible and what is physically possible. For example, it is physically impossible – in our Universe – that humans could survive on the surface of Mars unprotected.  But is it logically impossible? Well, we could imagine another Universe – a possible world – where human beings could breathe carbon dioxide and oxygen, and they could tolerate higher levels of radiation, extreme temperatures…and so on.  None of this is logically impossible.  There are no logical contradictions here, so there could be a world where all of this is possible. This plays well to Multiverse theorists, who capture the imagination with the notion of infinite worlds where – literally! – everything that could happen does happen in one Universe or another.  Think of it:  In some other Universe, you stopped reading one paragraph ago.  In another Universe, you didn’t even open the link.  In still another Universe, you wrote this post. As thrilling as those alternative Universes must be, there is no evidence that reality is composed this way.  Nevertheless, as a philosophical tool, the notion of possible worlds can be very useful, even to Christians. Here is another use of possible worlds:  They help us understand the difference between contingent and necessary beings. Let’s see – the device you are now viewing, which relays this post to you.  That exact device.  That device did not have to exist.  In point of fact, it did not exist for billions of years, and it will likely be junked and destroyed, ceasing to exist for the remaining trillions of years in the life of our Universe. The device is obviously contingent – it depends on some other being for its existence.  We can easily imagine a Universe where this device did not exist.  (In fact, it was this very Universe, 100 years ago). Necessary beings – if there are more than one – are entirely different.  They necessarily exist.  An example (if a matter of significant debate) is God. When you think about it, the classic, historical, traditional understanding of God is that He must exist, that He can’t fail to exist, that He just is existence itself.  He is a necessary being, perhaps the only necessary being. Ok.  Let that settle in. Now – God could have made any world, any of the possible worlds which philosophers dream of but cannot themselves create.  He had, perhaps, an infinite number of worlds to choose from. And He made this one. Then, He who – literally! – cannot die, cannot fail to exist, took the form of a contingent being.  He became flesh and dwelt among us.  He made Himself vulnerable to death, to annihilation, to the outer darkness. Behold, the philosopher’s mind collapses!  For, how can it be?  How can a necessary being humble Himself and make Himself vulnerable to non-existence?  How can He, who exists in any possible world, actually enter our world as one of us?  And why would He do such a thing? This is the Incarnation.  This is Christmas.