Originally published in 1969, the second edition of Professor Shackle's book has a fresh preface, an extra chapter and a number of additions to its bibliography. The extra chapter is concerned with the point at which one would decide to abandon an old policy and replace it with a new one. It is, in the words of the author, a further, rather radical development of the Stockholm sequence analysis. Professor Shackle examines how a decision can be rational only in a special sense, that of exploiting to the best present effect, on the decision-maker's state of mind, the scope afforded to imagination by what is known and by the gaps in that knowledge. The attempt made in this book to provide a theory of such decision has been called 'an existentialist economics'.