Not all concepts are learned in the same manner, nor by their acquisition are we equipped with the same sorts of instrumentalities. Take the concept of a unicorn: A fairly detailed description of one would be sufficient for you to learn this idea. Your knowledge would then allow me to expect several things of you: That you could then teach someone else this concept in the same way, i.e. by description; that you could pick out a unicorn from pictures of unicorns and other animals; that if asked, you could proceed to check whether there were any such things in existence; that, after discovering there were none, you would remain undaunted about the meaning of the concept and be the wiser as to its proper context of use, e.g. literature, mythology, and occasionally, philosophy. Here then is the sort of concept we can add to our lives or quite easily get along without. Not so with every concept. Some are indispensable. About one of these concepts St. Augustine said: "What then is time? If no one asks me, I know; if I want to explain it to a questioner, I do not know."1 Another such concept is that of person. Learning these concepts connects us to so many varied arenas of life, yet, unlike the situation with "unicorn", we seem unable to adequately render their meaning. But these grand concepts are distinguished in another way: they relate us in a different way altogether to the question of existence.
Recognizing the identity of a thing presupposes our knowledge of the kind of thing it is. But differences in the sort of concept involved play a significant role at this point. We can note and pick out the same unicorn before and after the existence question has been answered. Pictures, paintings and story-book descriptions make this possible. The situation changes with the concept of person. Here, the question of existence is taken care of differently and the character of judgements of identity reflect this special aspect of the matter.
In his recent book, The Coherence of Theism. 2 Professor R.G. Swinburne treates the issue of personal identity in a way which largely ignores these features peculiar to concepts like that of person. His work