the kind of thing that can be asserted or denied. "That all
men are mortal," "that Columbus discovered America," "that Charles I
died in his bed," "that all philosophers are wise," are propositions.
Not any series of words is a proposition, but only such series of words
as have "meaning," or, in our phraseology, "objective reference." Given
the meanings of separate words, and the rules of syntax, the meaning of
a proposition is determinate. This is the reason why we can understand
a sentence we never heard before. You probably never heard before the
proposition "that the inhabitants of the Andaman Islands habitually
eat stewed hippopotamus for dinner," but there is no difficulty in
understanding the proposition. The question of the relation between
the meaning of a sentence and the meanings of the separate words is
difficult, and I shall not pursue it now; I brought it up solely as
being illustrative of the nature of propositions.

We may extend the term "proposition" so as to cover the image-contents
of beliefs consisting of images. Thus, in the case of remembering a
room in which the window is to the left of the door, when we believe the
image-content the proposition will consist of the image of the window
on the left together with the image of the door on the right. We will
distinguish propositions of this kind as "image-propositions"
and propositions in words as "word-propositions." We may identify
propositions in general with the contents of actual and possible
beliefs, and we may say that it is propositions that are true or false.
In logic we are concerned with propositions rather than beliefs, since
logic is not interested in what people do in fact believe, but only
in the conditions which determine the truth or falsehood of possible
beliefs. Whenever possible, except when actual beliefs are in question,
it is generally a simplification to deal with propositions.

It would seem that image-propositions are more primitive than
word-propositions, and may well ante-date language. There is no reason
why memory-images, accompanied by that very simple belief-feeling which
we decided to be the essence of memory, should not have occurred before
language arose; indeed, it would be rash to assert positively that
memory of this sort does not occur among the higher animals. Our more
elementary beliefs, notably those that are added to sensation to make
perception, often remain at the level of images. For example, most of
the