e a peasant and think like a philosopher, or he will be as idle as a
savage. The great secret of education is to make physical and mental
exercises serve as relaxation for each other. At first our pupil had
nothing but sensations, and now he has ideas. Then he only perceived,
but now he judges. For from comparison of many successive or
simultaneous sensations, with the judgments based on them, arises a
kind of mixed or complex sensation which I call an idea.

The different manner in which ideas are formed gives each mind its
peculiar character. A mind is solid if it shape its ideas according to
the true relations of things; superficial, if content with their
apparent relations; accurate, if it behold things as they really are;
unsound, if it understand them incorrectly; disordered, if it fabricate
imaginary relations, neither apparent nor real; imbecile, if it do not
compare ideas at all. Greater or less mental power in different men
consists in their greater or less readiness in comparing ideas and
discovering their relations.

From simple as well as complex sensations, we form judgments which I
will call simple ideas. In a sensation the judgment is wholly passive,
only affirming that we feel what we feel. In a preception or idea, the
judgment is active; it brings together, compares, and determines
relations not determined by the senses. This is the only point of
difference, but it is important. Nature never deceives us; it is
always we who deceive ourselves.

I see a child eight years old helped to some frozen custard. Without
knowing what it is, he puts a spoonful in his mouth, and feeling the
cold sensation, exclaims, "Ah, that burns!" He feels a keen sensation;
he knows of none more so than heat, and thinks that is what he now
feels. He is of course mistaken; the chill is painful, but does not
burn him; and the two sensations are not alike, since, after
encountering both, we never mistake one for the other. It is not,
therefore, the sensation which misleads him, but the judgment based on
it.

It is the same when any one sees for the first time a mirror or optical
apparatus; or enters a deep cellar in mid-winter or midsummer; or
plunges his hand, either very warm or very cold, into tepid water; or
rolls a little ball between two of his fingers held crosswise. If he
is satisfied with describing what he perceives or feels, keeping his
judgment in abeyance, he cannot be mistaken. But when he decides