I described the rapid spread of the 'existentialist' label after 1945, but how do we determine when the label is appropriate? Who are to count as existentialists? I shall say a little by way of an answer before suggesting that we should not overtax ourselves in search of a precise one.

It is sometimes said that the reason it is hard to draw up an exact list is that existentialism is a mere 'tendency', rather than a coherent philosophy. Now while I do not want to minimize the differences between individual writers, I do hope to demonstrate that there is a coherent, definable philosophy of existentialism—no less, though perhaps no more, homogeneous than logical positivism, say, or pragmatism. The reason it is hard to place certain thinkers is not that the characterization of existentialism must be vague, but because they fit the characterization in some respects and...