From the preface:
I am of course not certain whether the two lectures which I here submit to the patient perusal or the possible refusal of my readers are, as I hope, the best I have produced so far; nor is this question, I admit, of any importance. But I wish to convey to my readers that I have worked hard to make them the best, since I myself have, in writing them, been able to learn things of great importance to myself.
I am grateful to have been able to do this in my 87th and 88th year, despite the drawbacks of failing memory.
A shorter version of the first lecture ["A World of Propensities: Two New Views of Causality"-Ed.] was given on August 24th, 1988 before the World Congress of Philosophy at Brighton, under the chairmanship of Professor Richard Hare. A shorter version of the second lecture ["Toward an Evolutionary Theory of Knowledge"-Ed.] was given on June 9th, 1989 before the Alumni of the School at the London School of Economics, under the chairmanship of its Director, Dr. I.G. Patel.
I never should have been able to write either of these lectures without the help of my Assistant, Melitta Mew.