FALLACIES IN DEDUCTIVE ARGUMENT.—PETITIO PRINCIPII AND IGNORATIO ELENCHI.
FORMAL OR ARISTOTELIAN INDUCTION.—INDUCTIVE ARGUMENT.
INDUCTIVE LOGIC, OR THE LOGIC OF SCIENCE.
THE DATA OF EXPERIENCE AS GROUNDS OF INFERENCE OR RATIONAL BELIEF.
II.—Tradition.—Hearsay Evidence .
III.—Method of Testing Traditional Evidence .
ASCERTAINMENT OF FACTS OF CAUSATION.
I.— Post Hoc ergo Propter Hoc .
II.—Meaning of "Cause".—Methods of Observation—Mill's Experimental Methods.
METHODS OF OBSERVATION.—SINGLE DIFFERENCE.
I.— The Principle of Single Difference.— Mill's "Canon".
II.—Application of the Principle.
METHODS OF OBSERVATION.—ELIMINATION.—SINGLE AGREEMENT.
I.— The Principle of Elimination.
II.— The Principle of Single Agreement.
III.— Mill's "Joint Method of Agreement and Difference".
METHODS OF OBSERVATION.—MINOR METHODS.
II.— Obstacles to Explanation.—Plurality of Causes and Intermixture of Effects.
III.— The Proof of a Hypothesis.
SUPPLEMENTARY METHODS OF INVESTIGATION.
I.— The Maintenance of Averages. — Supplement to the Method of Difference.
II.— The Presumption from Extra-Casual Coincidence.
PROBABLE INFERENCE TO PARTICULARS—THE MEASUREMENT OF PROBABILITY.
PREFACE.
In this little treatise two things are attempted that at first might appear incompatible. One of them is to put the study of logical formulæ on a historical basis. Strangely enough, the scientific evolution of logical forms, is a bit of history that still awaits the zeal and genius of some great scholar. I have neither ambition nor qualification for such a magnum opus, and my life is already more than half spent; but the gap in evolutionary research is so obvious that doubtless some younger man is now at work in the field unknown to me. All that I can hope to do is to act as a humble pioneer according to my imperfect lights. Even the little I have done represents work begun more than twenty years ago, and continuously pursued for the last twelve years during a considerable portion of my time.
The other aim, which might at first appear inconsistent with this, is to increase the power of Logic as a practical discipline. The main purpose of this practical science, or scientific art, is conceived to be the organisation of reason against error, and error in its various kinds is made the basis of the division of the subject. To carry out this practical aim along with the historical one is not hopeless, because throughout its long history Logic has been a practical science; and, as I have