A study of various central and connected topics in philosophical logic and the theory of meaning. There are important sections on the relation between linguistic and abstract entities, on necessity and convention, on meaning, sense and reference, and on entailment. Dr Lewy proposes a number of original solutions to problems which have been widely discussed in literature, and there is in particular a sharp and sustained criticism of conventionalism and reductionism. These are among the most difficult and intricate issues in contemporary philosophy, but Dr Lewy writes with great clarity and a minimum of technicality. Where his views are controversial they are explained and supported in a detail which makes it both possible and necessary for potential critics to state their disagreement precisely. The book should therefore be of value as an advanced textbook as well as an original contribution to philosophical logic.