Positivists have excelled at destructive criticism. This criticism has been useful for pruning away absurd and superfluous theories but it is liable to be used to prune away everything else. The latest exponents, the Logical Positivists, are no less adept at criticism than their predecessors. The doctrines of this school have been surrounded with an air of mystery and inquirers have been frightened off by alarming technical apparatus. We all know that the Logical Positivists had proved that everybody else talked nonsense, but we did not know what they themselves talked. Mr. A. J. Ayer's exposition of the doctrine, Language, Truth and Logic, is therefore welcome as it is simple,