On behaviourist lines, there is no important difference between proper names and what are called “abstract” or “generic” words. A child learns to use the word “cat”, which is general, just as he learns to use the word “Peter”, which is a proper name. But in actual fact “Peter” really covers a number of different occurrences, and is in a sense general. Peter may be near or far, walking or standing or sitting, laughing or frowning. All these produce different stimuli, but the stimuli have enough in common to produce the reaction consisting of the word “Peter”. Thus there is no essential difference, from a behaviourist point of view, between “Peter” and “man”. There are more resemblances between the various stimuli to the word “Peter” than between those to the word “man”, but this is only a difference of degree. We have not names for the fleeting particular occurrences which make up the several appearances of Peter, because they are not of much practical importance; their importance, in fact, is purely theoretic and philosophical. As such, we shall have a good deal to say about them at a later stage. For the present, we notice that there are many occurrences of Peter, and many occurrences of the word “Peter”; each, to the man who sees Peter, is a set of events having certain similarities. More exactly, the occurrences of Peter are _causally_ connected, whereas the occurrences of the word “Peter” are connected by similarity. But this is a distinction which need not concern us yet. General words such as “man” or “cat” or “triangle” are said to denote “universals”, concerning which, from the time of Plato to the present day, philosophers have never ceased to debate. Whether there are universals, and, if so, in what sense, is a metaphysical question, which need not be raised in connection with the use of language. The only point about universals that needs to be raised at this point is that the correct use of general words is no evidence that a man can think about universals. It has often been supposed that, because we can use a word like “man” correctly, we must be capable of a corresponding “abstract” idea of man, but this is quite a mistake. Some reactions are appropriate to one man, some to another, but all have certain elements in common. If the word “man” produces in us the reactions which are common but no others, we may be said to understand the word “man”. In learning geometry, one acquires the habit of avoiding special interpretations of such a word as “triangle”. We know that, when we have a proposition about triangles in general, we must not think specially of a right-angled triangle or any one kind of triangle. This is essentially the process of learning to associate with the word what is associated with _all_ triangles; when we have learnt this, we understand the word “triangle”. Consequently there is no need to suppose that we ever apprehend universals, although we use general words correctly.