Further, we know the truth “I am acquainted with this sense-datum.” It is hard to see how we could know this truth, or even understand what is meant by it, unless we were acquainted with something which we call “I.” It does not seem necessary to suppose that we are acquainted with a more or less permanent person, the same today as yesterday, but it does seem as though we must be acquainted with that thing, whatever its nature, which sees the sun and has acquaintance with sense-data. Thus, in some sense it would seem we must be acquainted with our Selves as opposed to our particular experiences. But the question is difficult, and complicated arguments can be adduced on either side. Hence, although acquaintance with ourselves seems probably to occur, it is not wise to assert that it undoubtedly does occur.
We may therefore sum up as follows what has been said concerning acquaintance with things that exist. We have acquaintance in sensation with the data of the outer senses, and in introspection with the data of what may be called the inner sense—thoughts, feelings, desires, etc. ; we have acquaintance in memory with things which have been data either of the outer senses or of the inner sense. Further, it is probable, though not certain, that we have acquaintance with Self, as that which is aware of things or has desires towards things.
In addition to our acquaintance with particular existing things, we also have acquaintance with what we shall call universals , that is to say, general ideas, such as “whiteness,” “diversity,” “brotherhood,” and so on. Every complete sentence must contain at least one word which stands for a universal, since all verbs have a meaning which is universal. We shall return to universals later on, in Chapter IX ; for the present, it is only necessary to guard against the supposition that whatever we can be acquainted with must be something particular and existent. Awareness of universals is called “conceiving,” and a universal of which we are aware is called a “concept.”