H. P. Grice and A. D. Woozley

 My thanks are due to Professor H. J. Paton, Mr H. H. Cox, and to Mr H. P. Grice, each of whom read the whole of or part of the manuscript and made many helpful criticisms, from which I have tried to profit; and to Mr B. G. Mitchell, who relieved me of the tedious task of compiling the index.