But we are met by the question what is meant by saying that one idea
affects another. The unravelment of this problem requires us to trace out
phenomena a little further.
Three elements go to make up an idea. The first is its intrinsic quality
as a feeling. The second is the energy with which it affects other
ideas, an energy which is infinite in the here-and-nowness of immediate
sensation, finite and relative in the recency of the past. The third
element is the tendency of an idea to bring along other ideas with it.
As an idea spreads, its power of affecting other ideas gets rapidly
reduced; but its intrinsic quality remains nearly unchanged. It is long
years now since I last saw a cardinal in his robes; and my memory of
their color has become much dimmed. The color itself, however, is not
remembered as dim. I have no inclination to call it a dull red. Thus, the
intrinsic quality remains little changed; yet more accurate observation
will show a slight reduction of it. The third element, on the other
hand, has increased. As well as I can recollect, it seems to me the
cardinals I used to see wore robes more scarlet than vermilion is, and
highly luminous. Still, I know the color commonly called cardinal is on
the crimson side of vermilion and of quite moderate luminosity, and the
original idea calls up so many other hues with it, and asserts itself so
feebly, that I am unable any longer to isolate it.
A finite interval of time generally contains an innumerable series
of feelings; and when these become welded together in association,
the result is a general idea. For we have just seen how by continuous
spreading an idea becomes generalised.
The first character of a general idea so resulting is that it is living
feeling. A continuum of this feeling, infinitesimal in duration, but
still embracing innumerable parts, and also, though infinitesimal,
entirely unlimited, is immediately present. And in its absence of
boundedness a vague possibility of more than is present is directly felt.
Second, in the presence of this continuity of feeling, nominalistic
maxims appear futile. There is no doubt about one idea affecting another,
when we can directly perceive the one gradually modified and shaping
itself into the other. Nor can there any longer be any difficulty about
one idea resembling another, when we can pass along the continuous field
of quality from one to the other and back again to the point which we had
marked.
Third, consider the insistency of an idea. The insistency of a past idea
with reference to the present is a quantity which is less the further
back that past idea is, and rises to infinity as the past idea is brought
up into coincidence with the present. Here we must make one of those
inductive applications of the law of continuity which have produced such
great results in all the positive sciences. We must extend the law of
insistency into the future. Plainly, the insistency of a future idea with
reference to the present is a quantity affected by the minus sign; for it
is the present that affects the future, if there be any effect, not the
future that affects the present. Accordingly, the curve of insistency is
a sort of equilateral hyperbola. [See the figure.] Such a conception is
none the less mathematical, that its quantification cannot now be exactly
specified.
[Illustration]
Now consider the induction which we have here been led into. This curve
says that feeling which has not yet emerged into immediate consciousness
is already affectible and already affected. In fact, this is habit, by
virtue of which an idea is brought up into present consciousness by a
bond that had already been established between it, and another idea while
it was still _in futuro_.
We can now see what the affection of one idea by another consists in.
It is that the affected idea is attached as a logical predicate to the
affecting idea as subject. So when a feeling emerges into immediate
consciousness, it always appears as a modification of a more or less
general object already in the mind. The word suggestion is well adapted
to expressing this relation. The future is suggested by, or rather is
influenced by the suggestions of, the past.