A belief, I should say, interpreted narrowly, is a form of words related to an emotion of one of several kinds. (I shall give a broader meaning later.) The emotion is different according as the belief embodies a reminiscence, a perception, an expectation, or something outside the experience of the believer. Moreover, a form of words is not essential. Where the emotion is present, and leads to action relevant to some feature of the environment, there may be said to be a belief. The fundamental test of a belief, of no matter what sort, is that it causes some event which actually takes place to arouse the emotion of expectedness or its opposite. I do not now attempt to decide what an emotion is. Dr. Watson gives a behaviouristic account of emotions, which would, if adopted, make my definition of “belief” purely behaviouristic. I have framed the definition so as not to involve a decision on the question of introspection. The subject of truth and falsehood may be subdivided as follows: A. _Formal Theory._--Given the meanings of the component words, what decides whether a sentence is true or false? B. _Causal Theory._--Can we distinguish between truth and falsehood by (_a_) their causes, (_b_) their effects? C. _Individual and Social Elements._--A statement is a social occurrence, a belief is something individual. How can we define a belief, and what is it when not composed of words? D. _Consistency and Truth._--Can we get outside the circle of beliefs or statements to something else which shows them true, not merely consistent? In other words, what possible relation is there between propositions and facts? It is very hard to disentangle these questions. The first question, as to formal theories, leads to the fourth, as to the relations of propositions to facts. _E.g._ “Brutus killed Cæsar” is true because of a certain fact; what fact? The fact that Brutus killed Cæsar. This keeps us in the verbal realm, and does not get us outside it to some realm of non-verbal fact by which verbal statements can be verified. Hence our fourth problem arises. But this leads us to our second problem, as to causes and effects of what is true or false, for it is here that we shall naturally look for the vital relation between propositions and facts. And here again we must distinguish between _thinking_ truly and _speaking_ truly. The former is an individual affair, the latter a social affair. Thus all our problems hang together.