ickly lost in
the few who have for a moment achieved it.

LECTURE XI. GENERAL IDEAS AND THOUGHT

It is said to be one of the merits of the human mind that it is capable
of framing abstract ideas, and of conducting nonsensational thought.
In this it is supposed to differ from the mind of animals. From Plato
onward the "idea" has played a great part in the systems of idealizing
philosophers. The "idea" has been, in their hands, always something
noble and abstract, the apprehension and use of which by man confers
upon him a quite special dignity.

The thing we have to consider to-day is this: seeing that there
certainly are words of which the meaning is abstract, and seeing that we
can use these words intelligently, what must be assumed or inferred, or
what can be discovered by observation, in the way of mental content to
account for the intelligent use of abstract words?

Taken as a problem in logic, the answer is, of course, that absolutely
nothing in the way of abstract mental content is inferable from the
mere fact that we can use intelligently words of which the meaning
is abstract. It is clear that a sufficiently ingenious person could
manufacture a machine moved by olfactory stimuli which, whenever a dog
appeared in its neighbourhood, would say, "There is a dog," and when
a cat appeared would throw stones at it. The act of saying "There is a
dog," and the act of throwing stones, would in such a case be equally
mechanical. Correct speech does not of itself afford any better evidence
of mental content than the performance of any other set of biologically
useful movements, such as those of flight or combat. All that is
inferable from language is that two instances of a universal, even when
they differ very greatly, may cause the utterance of two instances
of the same word which only differ very slightly. As we saw in the
preceding lecture, the word "dog" is useful, partly, because two
instances of this word are much more similar than (say) a pug and a
great dane. The use of words is thus a method of substituting for two
particulars which differ widely, in spite of being instances of the same
universal, two other particulars which differ very little, and which
are also instances of a universal, namely the name of the previous
universal. Thus, so far as logic is concerned, we are entirely free to
adopt any theory as to general ideas which empirical observation may
recommend.

Berkeley and Hume made a vigorous