In the agrarian economy each market is clearly defined in time and space; in the industrial economy there is no spatial restriction – commodities are exchanged right across the world – and there is no single defined period over which all transactions must be completed. Buyers and sellers make contracts for whatever period is mutually agreeable.
I have come to believe that economists have built a discipline for a world which has largely vanished, and that is why we have nothing sensible to say about the challenges that face the world economy today.