the avoiding reaction or the
attentive reaction that an unimportant stimulus at first arouses,
these reactions being rather a nuisance when they are unnecessary. On
the whole, the law of combination seems to fill the bill very well. It
explains what the law of exercise left unexplained. It always brings
in the law of exercise as an ally, and, in explaining substitute
response, it brings in the law of effect, which however, as we saw
before, may be a sub-law under the law of exercise. These two, or
three laws, taken together, give an adequate analysis of the whole
process of learning.

The Law of Combination in Recall

Unitary response to multiple stimuli is important in recall as well as
in learning. The clearest case of this is afforded by "controlled
association". [Footnote: See p. 381.]

In an opposites test, the response to the stimulus word "long" is
aroused partly by this stimulus word, and partly by the "mental set"
for opposites. There are two lines of influence, converging upon the
response, "long--short" (of which only the word "short" may be
spoken): one line from the stimulus word "long", and the other from
the mental set for pairs of opposite words. The mental set for
opposites tends to arouse any pair of opposites; the word "long" tends
to arouse any previously observed group of words of which "long" is a
part. The mental set, an internal stimulus, and the stimulus word
coming from outside, converge or combine to arouse one particular
response.

The mental set for adding has previously exercised {414} linkages with
the responses composing the addition table, while the mental set for
multiplication has linkages with the responses composing the
multiplication table. When the set for adding is active, a pair of
numbers, seen or heard, together with this internal stimulus of the
mental set, arouses the response that gives the sum; but when the
multiplying set is active, the same pair of numbers gives the product
as the response. All thinking towards any goal is a similar instance
of the law of combination.

The Laws of Learning in Terms of the Neurone

We have good evidence that the brain is concerned in learning and
retention. Loss of some of the cortex through injury often brings loss
of learned reactions, and the kind of reactions lost differs with the
part of the cortex affected. Injury in the occipital lobe brings loss
of visual knowledge, and injury in the neighborhood of the auditory
sense-