A. J. Ayer abstraction activity actual answer argument become bourgeois called capitalist cardinal numbers category-mistakes communism communist conception concerned conclusions consists contradictions criticism demonstration Descartes dialectical materialism dialectical materialist dialectics distinct doctrine economic empirical sciences Engels evidendy example existence experience expressions fact formal logic generalisations Hare Hobbes human relations Hume idealist ideals ideas independendy individuals inquiry interests investigation kind knowledge labour language language games laws linguistic philosophy logical behaviour Marx Marxism material materialist means merely metaphysical method mind mode moral judgments moral principles naturalistic fallacy objects organisation particular philo philosophical theory political positivist practical Principia Principia Mathematica problems propositions purposes questions R. M. Hare reason relations of production religion Russell Ryle scientific sensations sense sense-data simply social production socialist society solipsism statements techniques things thought tion truth universalisable universe value judgments verification principle verified Wittgenstein words