To understand this family of cases it will again be helpful to
consider an analogous case drawn from facial expressions.
There is a family of friendly facial expressions.
Suppose we had asked, “What feature is it that
characterizes a friendly face?”
At first one might think that there are certain
traits which one might call friendly traits,
each of which makes the face look friendly to a certain degree, and which
when present in a large number constitute the friendly
expression.
This idea would seem to be borne out by our common speech,
talk
ing
106.
of
“friendly eyes”, “friendly mouth”,
etc.
But it is easy to see that the same eyes of which we say they make a
face look friendly, do not look friendly, or even
look
unfriendly, with certain other wrinkles of the forehead, lines round the
mouth, etc.
Why then do we ever say that it is these eyes which look
friendly?
Isn't it wrong to say that they characterize the face as
friendly, for if we say they do so “under certain
circumstances” (these circumstances being the other features
of the face) why did we single out the one feature from amongst the
others?
The answer is that in the wide family of friendly faces there is what
one might call a main branch characterized by a certain kind of eyes,
another by a certain kind of mouth, etc.; although in the
large family of unfriendly faces we meet these same eyes when they
don't mitigate the unfriendliness of the
expression. ‒ ‒
There is further the fact that when we notice the friendly expression
of a face, our attention, our gaze, is drawn to a particular feature in
the face, the “friendly eyes” or the “friendly
mouth”, etc., and that it does not rest on other
features although these too are responsible for the friendly
expression.