ughgoing acquaintance with the
particular field of inquiry. Thinking aims to explain the
relations between facts, and an intimate acquaintance with
facts involved in a given situation is prerequisite to any
generalization whatsoever.

While the native fertility of given minds cannot be controlled,
suggestions can be controlled indirectly. Suggestions
arise from the data at hand, but the data themselves change
under more precise conditions of observation, and the suggestions
that arise from them change in consequence. The
whole elaborate apparatus of science, its instruments of
precision, are designed to yield an exact determination of the
precise nature of the data at hand. The scientist attempts to
prevent "reading-in" of meanings. "Reading-in" of meanings
may be due to various causes. In the first place there
may be purely physical causes: a dim light, a fog, a cracked
window-pane are examples of how ordinary observation may
lead us astray. Again, physiological causes may be at work
to distort sensations: imperfection's in the sense organs,
fatigue, illness, and the like are examples. But not least among
the causes of error must be set psychological causes. That is,
we read facts differently in the light of what we fear or hope,
like or dislike, expect or recall. We see things the way we
want them to be, or the way previous experience has taught
us to expect them to be.

Both physiological and psychological causes may be checked
up by instruments. Indeed, one of the chief utilities of
instruments of precision is that they do serve to check up personal
error. They prevent scientific inquirers from reading in
meanings to which they are led by hope, fear, preference, or
aversion. They help us to see the facts as they are, not as for
various social and personal reasons we want or expect them
to be. They help to give precise and permanent impressions
which are not dependent for their discovery or for their preservation
on the precariousness of human observation or memory.

CLASSIFICATION. Next only in importance to accurate
observation of the facts is their classification. Objects of
experience as they come to us through the senses appear in a
sequence which is random and chaotic. But in order to deal
effectively with our experience we must arrange facts according
to their likenesses and differences. Whenever we discover
certain striking similarities between facts, we classify
them, place them in a class, knowing t