MANY years ago I read about a book by a nineteenthcentury German mathematician, Felix Klein, called Elementary Mathematics from an Advanced Standpoint. I never read it, but the title stuck in my mind. The present book could perhaps be subtitled Elementary Social Science from an Advanced Standpoint.

Or should it be the other way around – advanced social science from an elementary standpoint? In that case, my model would be a short and wonderful book by Richard Feynman, QED, an introduction to quantum electrodynamics for the general public. The comparison is not as presumptuous as one might think. On the one hand, Feynman's ability to go to the core of a subject, without technicalities but also without loss of rigor, may be unsurpassed in the history of science and is in any case beyond mine. On the other, quantum electrodynamics is more arcane than any of the topics discussed here. On balance, therefore, the reader may find my exposition just as intelligible.

The purpose of the book is reflected in its title: to introduce the reader to causal mechanisms that serve as the basic units of the social sciences. Though not a do-it-yourself kit, it might serve as a read-it-yourself kit for further study. The reader should be wary of the chapter on reinforcement, a topic about which I know little but which is too important to be neglected. I hope what I say is correct, but people who know more about it may find it superficial.