Logic (Hurley Chapter 1) Joy

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logic

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"... the organized body of knowledge, or science, that evaluates arguments."
The study of the methods and principles of evaluating arguments.

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argument

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A group (two or more) of statements which contain at least one premise statement that claims to support a conclusion statement.

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statement

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A claim or assertion that is either true of false.

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conclusion indicators

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therefore, accordingly, entails that, hence, thus, consequently, implies that, so... (see p. 3 for more)

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premise indicators

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since, because, for, given that... (see p. 3 for more)

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deductive argument

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If the arguer thinks that his/her conclusion follows with absolute certainty from the premise(s), that is called a DEDUCTIVE argument. (An argument for which the arguer claims that the premises lead conclusively to the conclusion.) (The arguer claims that if the premise(s) are true, then the conclusion must be true.) (The arguer claims that it is impossible for the conclusion to be false given that [if] the premises are true.)

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valid deductive argument

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The premises do lead conclusively to the conclusion. (if the premise(s) are true, then the conclusion must be true. ) (It is impossible for the conclusion to be false given that the premises are true.)

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some inductive argument types

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prediction, analogy, generalization, based on authority, based on signs, causal inference ...

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sound argument

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a deductive argument that is (1) valid and (2) has all true premises

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substitution instance

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the result from uniformly substituting terms or statements in place of the letters in an argument's form

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invalid deductive argument

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Although the arguer has claimed the premises necessitate the conclusion (it cannot be false if the premises are true), this is not actually the case. That is, it is possible for the conclusion to be false when the premises are true.

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inductive argument

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An argument for which it is claimed that it is improbable for the conclusion to be false if the premises are true. An argument for which it is claimed that the premises make the conclusion probable.

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strong inductive argument

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It is improbable that the conclusion is false given that the premises are true . . . . If the premises are true or taken as "given" then the conclusion is, indeed, probably true. . . ." The premises when true or taken as given, make the conclusion more than 50% likely.

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weak inductive argument

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Although the arguer claims the conclusion follows with more than 50% likelihood from the premises, it does not.

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cogent argument

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An inductive argument that is (1) strong and (2) has all true premises.

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unsound argument

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a deductive argument that either does not have all true premises or is invalid (or both).

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some deductive argument types

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arguments based on mathematics, arguments from definition, categorical syllogisms, hypothetical syllogisms, disjunctive syllogisms. . .