The essays in this collection are taken from articles and lectures that I have written or delivered over many years – some of which I hadn't looked at in quite a while. Putting them together I am struck by the recurrence of certain themes. This shouldn't be surprising since I have been thinking about these subjects for a long time. They occur in somewhat different contexts and reflect the evolution of my thoughts on the relation of science to other human activities.

Since some of the articles were written years ago, I have occasionally included footnotes to update matters where the situation has dramatically changed; but otherwise I have pretty much left things the way they were because that was the way I thought about them at the time.

What is more problematic is that in the originals there are paragraphs and even sections that are repeated from one article to the next. As with itinerant actors and musicians over the centuries, each performance is pieced together from those that have come before – self-plagiarism. But each is presented in a new package and sometimes the package is as interesting as the content.

So I've deleted extended repetitions; also in some of the essays I have excised sections that, in my opinion, don't contribute to the main line of thought and, sometimes, are discussed in other essays.