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PROFESSOR OF LOGIC, ETC. IN OWENS COLLEGE, MANCHESTER.

London ;
MACMILLAN AND CO.

1869.

[The Right of Translation and Reproduction is reserved.]

LONDON:

R. CLAY, SONS, AND TAYLOR, PRINTERS,

BREAD STREET HILL.

Вь J53 S

PREFACE.

In this small treatise I wish to submit to the

judgment of those interested in the progress of logical science a notion which has often forced itself upon my mind during the last few years. All acts of reasoning seem to me to be different cases of one uniform process, which may perhaps be best described as the substitution of similars. This phrase clearly expresses that familiar mode in which we continually argue by analogy from like to like, and take one thing as a representative of another. The chief difficulty consists in showing that all the forms of the old logic, as well as the fundamental rules of mathematical reasoning, may be explained upon the same principle; and it is to this difficult task I have devoted the most attention. The new and wonderful results of the late Dr.

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