285

CHAPTER III.

Ascertainment of Facts of Causation. (1) _Post Hoc Ergo
Propter Hoc._ (2) Meaning of Cause--Methods of Observation
--Mill's Experimental Methods, 295

CHAPTER IV.

Method of Observation--Single Difference. (1) The Principle
of Single Difference. (2) Application of the Principle, 308

CHAPTER V.

Methods of Observation--Elimination--Single Agreement.
(1) The Principle of Elimination. (2) The Principle of
Single Agreement. (3) Mill's "Joint Method of Agreement
and Difference," 318

CHAPTER VI.

Methods of Observation--Minor Methods. (1) Concomitant
Variations. (2) Single Residue, 329

CHAPTER VII.

The Method of Explanation. (1) The Four Stages of Orderly
Procedure. (2) Obstacles to Explanation--Plurality of Causes
and Intermixture of Effects. (3) The Proof of a Hypothesis, 334

CHAPTER VIII.

Supplementary Methods of Investigation. (1) The Maintenance
of Averages--Supplement to the Method of Difference.
(2) The Presumption from Extra-Casual Coincidence, 351

CHAPTER IX.

Probable Inference to Particulars--The Measurement of
Probability, 362

CHAPTER X.

Inference from Analogy, 367

INTRODUCTION.

I.--THE ORIGIN AND SCOPE OF LOGIC.

The question has sometimes been asked, Where should we begin in Logic?
Particularly within the present century has this difficulty been felt,
when the study of Logic has been revived and made intricate by the
different purposes of its cultivators.

Where did the founder of Logic begin? Where did Aristotle begin? This
seems to be the simplest way of settling where we should begin, for
the system shaped by Aristotle is still the trunk of the tree, though
there have been so many offshoots from the old stump and so many
parasitic plants have wound themselves round it that Logic is now
almost as tangled a growth as the Yews of Borrowdale--

An intertwisted mass of fibres serpentine
Upcoiling and inveterately convolved.

It used to be said that Logic had remained for two thousand years
precisely as Aristotle left it. It was an example of a science or
art perfected at one stroke by the genius of its first inventor.
The bewildered s