Royal
logicians spoke of it as equivalent to the art of thinking. Even
popularly, accuracy of classification, and the extent of command over
premisses, are thought clearer signs of logical powers than accuracy of
deduction. On the other hand, the definition of logic as a 'science
treating of the operations of the understanding in the search of truth,'
though wide enough, would err through including truths known from
intuition; for, though doubtless many seeming intuitions are processes
of inference, questions as to what facts are _real intuitions_ belong
to Metaphysics, not to Logic.

Logic is the science, not of Belief, but of Proof, or Evidence. Almost
all knowledge being matter of inference, the fields of Logic and of
Knowledge coincide; but the two differ in so far that Logic does not
find evidence, but only judges of it. All science is composed of data,
and conclusions thence: Logic shows what relations must subsist between
them. All inferential knowledge is true or not, according as the laws of
Logic have been obeyed or not. Logic is Bacon's _Ars Artium_, the
science of sciences. Genius sometimes employs laws unconsciously; but
only genius: as a rule, the advances of a science have been ever found
to be preceded by a fuller knowledge of the laws of Logic applicable to
it. Logic, then, may be described as the science of the operations of
the understanding which aid in the estimation of evidence. It includes
not only the process of proceeding from the known to the unknown, but,
as auxiliary thereto, Naming, Definition, and Classification.
Conception, Memory, and other like faculties, are not treated by it; but
it presupposes them. Our object, therefore, must be to analyse the
process of inference and the subsidiary operations, besides framing
canons to test any given evidence. We need not, however, carry the
analysis beyond what is necessary for the practical uses of Logic; for
one step in analysis is good without a second, and our purpose is simply
to see the difference between good and ill processes of inference.
Minuter analysis befits Metaphysics; though even that science, when
stepping beyond the interrogation of our consciousness, or rather of our
memory, is, as all other sciences, amenable to Logic.

BOOK I

NAMES AND PROPOSITIONS.

CHAPTER I.

ON THE NECESSITY OF COMMENCING WITH AN ANALYSIS OF LANGUAGE IN LOGIC.

The fact of Logic being a portion of the art of thinking, and of
thought'