In the present chapter I wish to consider certain words which occur in the secondary language and in all higher languages, but not in the object-language. The words in question are characteristic of logic. I shall especially consider "true", "false", "not", "or", "some", and "all". We know from logic that these terms cannot all be defined, but that it is to a large extent optional which shall be defined in terms of which. Our problem being one of theory of knowledge, we are less concerned with the definition of these terms than with the way in which we come to know propositions in which they occur.