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Chapter 1: Logic

Chapter 1: Logic

pp. 1-10

Authors

, University of Toronto
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Summary

Logic is about good and bad reasoning. In order to talk clearly about reasoning, logicians have given precise meanings to some ordinary words. This chapter is a review of their language.

ARGUMENTS

Logicians attach a special sense to the word argument. In ordinary language, it usually takes two to argue. One dictionary defines an argument as:

  • A quarrel.

  • A discussion in which reasons are put forward in support of and against a proposition, proposal, or case.

  • A point or series of reasons presented to support a proposition which is the conclusion of the argument.

  • Definition (3) is what logicians mean by an argument.

    Reasoning is stated or written out in arguments. So logicians study arguments (in sense 3).

    An argument thus divides up into:

    A point or series of reasons which are called premises, and a conclusion.

    Premises and conclusion are propositions, statements that can be either true or false. Propositions are “true-or-false.”

    GOING WRONG

    The premises are supposed to be reasons for the conclusion. Logic tries to understand the idea of a good reason.

    We find arguments convincing when we know that the premises are true, and when we see that they give a good reason for the conclusion.

    So two things can go wrong with an argument:

  • ▪ the premises may be false.

  • ▪ the premises may not provide a good reason for the conclusion.

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