philosophy

Deduction vs. Induction

or

Deductive Logic vs. Inductive Logic

1. Deduction aims at certainty and, Induction aims at a high when it is successful, attains it. probability.

2. Given the truth of the premises, Given the truth of the premises, the the conclusion is necessarily true. conclusion is only likely and might be F.

3. A deductive argument is valid or There is a continuum from weak up to invalid, period, nothing between. stronger, with evaluation between.

4. A valid deductive argument is A strong induction can lead from true truth-preserving: any truth in the premises to a false conclusion. premises appears in the conclusion.

5. A valid deduction is nonampliative: All inductions are ampliative: the the information in the conclusion is information in the conclusion goes the same as the information in some beyond (is more than, and new) the of or all the premises. information in the premises (think of interpolation and extrapolation).

6. The information in the conclusion The information in the conclusion is is a rearranged repetition of the not a repetition of the information in information in some of or all the the premises. premises.

7. All invalid deductions are inductions. All inductions are invalid deductions.

8. Because it is truth-preserving and Because it is not truth-preserving, nonampliative, deduction is risk-free; induction is risky; but it can yield new but it does not yield new information. information. (We use newly developed drugs even though the probability that they work and are safe is only 95% -- we sometimes suffer as a result.)

9. The value of deduction: the exposing, The value of induction: progress in emancipation, or revelation of the knowledge (as in science). ‘hidden’ meanings of the premises. (Mathematics.)