all the powers at our disposal. In the case of the automobile, we call
to mind other accidents and the causes of them; we remember that once
the spark-plug played out, so we test this hypothesis. At another time
some dust got into the carburetor, so we test this. So we go on,
calling up possible causes and applying appropriate remedies until the
right one is found and the engine is started. In bringing to bear upon
the problem facts from our past experience, we form a series of
judgments. In the case of the problem as to what college to attend, we
might form these judgments: this college is nearer home; that one has a
celebrated faculty; this one has good laboratories; that one is my
father's alma mater. So we might go on, bringing up all the facts
regarding the problem and fitting each one mentally to see how it
works. Note that this utilization of ideas should not consist merely of
fumbling about in a vague hope of hitting upon some solution. It must
be a systematic search, guided by carefully chosen ideas. For example,
"if the clock on the mantle-piece has stopped, and we have no idea how
to make it go again, but mildly shake it in the hope that something
will happen to set it going, we are merely fumbling. But if, on moving
the clock gently so as to set the pendulum in motion, we hear it
wobbling about irregularly, and at the same time observe that there is
no ticking of any kind, we come to the conclusion that the pendulum has
somehow or other escaped the little catch that connects it with the
mechanism, we have been really thinking. From the fact that the
pendulum wobbles irregularly, we infer that it has lost its proper
catch. From the fact that there is no ticking, we infer the same thing,
for even when there is something wrong with the clock that will prevent
it from going permanently, if the pendulum is set in motion by force
from without it will tick for a few seconds before it comes to rest
again. The important point to observe is that there must be inference.
This is always indicated by the word _therefore_ or its equivalent. If