the case of
words of our present sort than in any other case.

There is no very great difference between such words as we have just
been considering and words denoting qualities, such as "white" or
"round." The chief difference is that words of this latter sort do not
denote processes, however brief, but static features of the world. Snow
falls, and is white; the falling is a process, the whiteness is not.
Whether there is a universal, called "whiteness," or whether white
things are to be defined as those having a certain kind of similarity to
a standard thing, say freshly fallen snow, is a question which need
not concern us, and which I believe to be strictly insoluble. For our
purposes, we may take the word "white" as denoting a certain set of
similar particulars or collections of particulars, the similarity being
in respect of a static quality, not of a process.

From the logical point of view, a very important class of words
are those that express relations, such as "in," "above," "before,"
"greater," and so on. The meaning of one of these words differs very
fundamentally from the meaning of one of any of our previous classes,
being more abstract and logically simpler than any of them. If our
business were logic, we should have to spend much time on these words.
But as it is psychology that concerns us, we will merely note their
special character and pass on, since the logical classification of words
is not our main business.

We will consider next the question what is implied by saying that a
person "understands" a word, in the sense in which one understands
a word in one's own language, but not in a language of which one is
ignorant. We may say that a person understands a word when (a) suitable
circumstances make him use it, (b) the hearing of it causes suitable
behaviour in him. We may call these two active and passive understanding
respectively. Dogs often have passive understanding of some words, but
not active understanding, since they cannot use words.

It is not necessary, in order that a man should "understand" a word,
that he should "know what it means," in the sense of being able to say
"this word means so-and-so." Understanding words does not consist in
knowing their dictionary definitions, or in being able to specify the
objects to which they are appropriate. Such understanding as this may
belong to lexicographers and students, but not to ordinary mortals
in ordinary life. Understanding language is