without regard to possible {469} variations of the
perceptive response of inference, there are at least different
varieties of the exploratory process leading up to inference. The
situation that arouses reasoning differs from one case to another, the
motive for engaging in this rather laborious mental process differs,
and the order of events in the process differs. There are several main
types of reasoning, considered as a process of mental exploration.

1. Reasoning out the solution of a practical problem.

A "problem" is a situation for which we have no ready and successful
response. We cannot successfully respond by instinct or by previously
acquired habit. We must _find out_ what to do. We explore the
situation, partly by the senses and actual movement, partly by the use
of our wits. We observe facts in the situation that recall previous
experiences or previously learned rules and principles, and apply
these to the present case. Many of these clues we reject at once as of
no use; others we may try out and find useless; some we may think
through and thus find useless; but finally, if our exploration is
successful, we observe a real clue, recall a pertinent guiding
principle, and see the way out of our problem.

Two boys went into the woods for a day's outing. They climbed about
all the morning, and ate their lunch in a little clearing by the side
of a brook. Then they started for home, striking straight through the
woods, as they thought, in the direction of home. After quite a long
tramp, when they thought they should be about out of the woods, they
saw clear space ahead, and, pushing forward eagerly, found themselves
in the same little clearing where they had eaten their lunch!
Reasoning process No. 1 now occurred: one of the boys _recalled_ that
when traversing the woods without any compass or landmark, the
traveller is very likely to go in a circle; inference, "That is what
we have done and {470} we probably shall do the same thing again if we
go ahead. We may as well sit down and think it over."

Mental exploration ensued. "How about following the brook?" "That
won't do, for it flows down into a big swamp that we couldn't get
through". "How about telling directions by the sun?" "But it has so
clouded over that you can't tell east from west, or north from south."
"Yes, those old clouds! How fast they are going! They seem to go
straight enough." "Well, say! How about following the clouds? If we
keep on goin