PHI 1600 Deductive Inductive Notes PDF

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PHI 1600 Deductive Inductive Notes...

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http://baruchlogic.org/ Pass:2WXzDc8R Unit 1

Deductive and inductive arguments differ in the kind of support that the argument is supposed to provide for the conclusion. In a deductive argument, the premises are meant to provide conclusive, indisputable reasons for accepting the conclusion: if the premises are true, the conclusion must be true, and there’s no possible way for it to be false. An inductive argument, on the other hand, is one in which the premises are intended to provide evidential support for the conclusion, but not definitive proof. Section 2 Deductive

● A valid argument may have false premises. When judging validity, we simply assume that the premises are true, even if we know they are false. ● A valid argument may have a false conclusion. A valid argument must have good reasoning, but if you start from false premises, then you can end up at a false conclusion, even if your reasoning is valid. ● A sound argument must have true premises. Soundness is validity plus true premises, so this one is self-evident. ● A sound argument must have a true conclusion. This follows from the fact that a sound argument must have true premises, and it must be valid. Since validity preserves truth, a sound argument will also have a true conclusion. ● An argument may be invalid even if every statement in the argument is true. Inductive ● A strong argument may have false premises. When judging strength, we simply assume that the premises are true, even if we know they are false. ● A strong argument may have a false conclusion. Like deductive arguments, a strong argument might have a false conclusion if it starts from false premises. Unlike a deductive argument, a strong argument can have a false conclusion even if it starts with true premises (strong arguments only make the conclusion probable, not certain). ● A cogent argument must have true premises. Cogency is strength plus true premises, so this one is self-evident. ● A cogent argument does not have to have a true conclusion. Since inductive reasoning is probabilistic, even strong inductive reasoning can sometimes lead to a false conclusion. ● An argument may be weak even if every statement in the argument is true. As with deductive reasoning, if an argument does not follow a logical “train of thought,” but instead consists of unconnected (but true) statements, then it would not be a strong argument, even if all the statements happened to be truths.

The relation between these concepts can be symbolized in a table: THE PREMISES SUPPORT THE CONCLUSION

THE PREMISES ARE TRUE AND SUPPORT THE CONCLUSION

DEDUCTIVE ARGUMENT

Valid (the premises, if true, provide definitive proof of the conclusion)

Sound

INDUCTIVE ARGUMENT

Strong (the premises, if true, provide good evidence for the conclusion)

Cogent

Steps To Arguments 1. Defining arguments 2. Recognizing Arguments 3. Evaluating Arguments 4. Evaluating Deduction 5. Evaluating Induction

Valid Proof? Invalid Multiple Statements No Not an Argument

Ye s

Inferred Conclusi on No

Not an Argument

Science: Descriptive/ Factual Logic: Evaluate/ Normative * Rational justified 2.2 Fallacies of Relevance 2.3 Fallacies of Evidence 2.4 Fallacies of Significance Informal Fallacies (1600.rocks/slides2)

Sou nd

Unsoun d Strong Evidence ? Uncog ent

Cogent...