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INTRODUCTION.

LESSON I.

DEFINITION AND SPHERE OF THE SCIENCE.

LOGIC may be most briefly defined as the Science of Reasoning. It is more commonly defined, however, as the Science of the Laws of Thought, and some logicians think it desirable to specify still more accurately that it is the Science of the Formal, or of the Necessary Laws of Thought. Before these definitions can be of any real use to us we must come to a clear understanding as to the meaning of the expressions; and it will probably appear that there is no great difference between them.

By a Law of Thought we mean a certain uniformity or agreement which exists and must exist in the modes in which all persons think and reason, so long as they do not make what we call mistakes, or fall into self-contradiction and fallacy. The laws of thought are natural laws with which we have no power to interfere, and which are of course not to be in any way confused with the artificial laws of a country, which are invented by men and can be altered by them. Every science is occupied in detecting and describing the natural laws which are inflexibly observed

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