knowledge, but simply natural events with no more knowledge status
than (say) a shower. "Let them [the realists] try the experiment of
conceiving perceptions as pure natural events, not cases of awareness or
apprehension, and they will be surprised to see how little they miss."*
I think he is right in this, except in supposing that the realists will
be surprised. Many of them already hold the view he is advocating, and
others are very sympathetic to it. At any rate, it is the view which I
shall adopt in these lectures.

* Dewey, "Essays in Experimental Logic," pp. 253, 262.

The stuff of the world, so far as we have experience of it, consists, on
the view that I am advocating, of innumerable transient particulars such
as occur in seeing, hearing, etc., together with images more or less
resembling these, of which I shall speak shortly. If physics is true,
there are, besides the particulars that we experience, others, probably
equally (or almost equally) transient, which make up that part of the
material world that does not come into the sort of contact with a
living body that is required to turn it into a sensation. But this topic
belongs to the philosophy of physics, and need not concern us in our
present inquiry.

Sensations are what is common to the mental and physical worlds; they
may be defined as the intersection of mind and matter. This is by no
means a new view; it is advocated, not only by the American authors I
have mentioned, but by Mach in his Analysis of Sensations, which was
published in 1886. The essence of sensation, according to the view I am
advocating, is its independence of past experience. It is a core in our
actual experiences, never existing in isolation except possibly in very
young infants. It is not itself knowledge, but it supplies the data for
our knowledge of the physical world, including our own bodies.

There are some who believe that our mental life is built up out of
sensations alone. This may be true; but in any case I think the only
ingredients required in addition to sensations are images. What images
are, and how they are to be defined, we have now to inquire.

The distinction between images and sensations might seem at first sight
by no means difficult. When we shut our eyes and call up pictures of
familiar scenes, we usually have no difficulty, so long as we remain
awake, in discriminating between what we are imagining and what is
really seen. If we imagine some piece of