It is good that Professor Ayer has written this book,1 if only because it is a rounded treatment of a subject in one of the Wittgensteinian ways of handling philosophy. There have been at least two other works of recent times that have also provided rounded treatments of a philosophical problem in a Wittgensteinian way. There are of course differences of outlook, opinion, and method in all of these, but this does not prevent them from being different versions of Wittgensteinianism. Perhaps Professor Ayer does not regard himself as a Wittgensteinian, but this is a matter of classification, and it is legitimate, if we want to, to put together all treatments that are dominated by one of the chief Wittgensteinian trends (provided they are not discordant with other main trends). Even so, he is the least Wittgensteinian of the Wittgensteinians.