Induction ~ Deduction

Induction ~ Deduction1In this lectureComparisonInductionDeduction Resources

2Comparison: Induction - DeductionIn a broad way, the deductive reasoning (or argument) begins with the general and works its way to the specific while inductive begins with the specific and moves to the general. Of course, thats a simplistic overview, so lets take a look at how it works. 3Induction John cuts his lawn every week. Others dont cut their lawns every week. Lawns dont have to be cut every week.

The inductive process begins with observations, then analyzes the observations to see if there is a pattern. If a pattern is discovered, an inference can be made. The inference leads to a prediction (conclusion).

In this example, it may be true that people in the neighborhood cut their lawns every week; however, more observations done over a larger sample would show that is not the case everywhere, and the conclusion would not be confirmed.

Inductive reasoning is strong if the observations are sufficient and unbiased, if the classification (analysis) is sound, if the inference is credible, and if the conclusion can be confirmed. One of the key weaknesses of inductive reasoning is our propensity to use small samples. For instance, its not uncommon for Ms. X to cast a wary glance at Ms. Y, who is buying candy with food stamps. Ms. X is making an assumption that Ms. Y squanders the public assistance she is receiving. Ms. X may then infer that inappropriate use of public assistance is common and reach the conclusion that anyone who receives public assistance must be scamming.

The single observation is not sufficient to make any such inference; even 10 or 20 or 30 observations would not be enough given the size of public assistance programs in the US. It may be that Ms. Y is providing a very rare treat for her children. Or she may be having a really bad day and need some sweet comfort. Even if Ms. Y was using food stamps inappropriately, it is not possible to leap to the conclusion that all people who use food stamps are scamming the system in some way.

Watch out for unwarranted leaps in arguments.

4Deduction Lawns should be cut every week. T1 John cuts his lawn every week. T2 Others dont cut lawns every week. Claim is not confirmed.

Unlike induction, which begins with specific observations and works its way up to a conclusion, deduction begins with a conclusion (AKA claim, hypothesis, theory, thesis, position) and then sets out to confirm or deny the hypothesis. Deductive reasoning can be used to determine the validity of an inductive conclusion.

Deductive reasoning is a generally strong form of reasoning because it sets up numerous tests or experiments or studies to determine whether an idea is valid or not. Deductive reasoning is often thought of as a scientific process or science can be thought of as a process of deductive reasoning.

For example, a social scientist may have a theory that fraud is rampant among food stamp recipients. The researcher sets up a number of ways to test the theory. The data from the research is analyzed, and its discovered that there is some fraud, but it is not nearly as prevalent as was imagined. In fact, the amount of fraud may not be beyond the expected norms for a major program of any kind.

When considering deductive arguments, be sure to look for the types of tests and evidence used to confirm or refute the hypothesis.

5ResourcesDeductive Reasoninghttp://changingminds.org/disciplines/argument/types_reasoning/deduction.htm Inductive Logichttp://plato.stanford.edu/entries/logic-inductive/ Inductive Reasoninghttp://changingminds.org/disciplines/argument/types_reasoning/induction.htm More on Logichttp://www.psych.utah.edu/gordon/Classes/Psy4905Docs/PsychHistory/Cards/Logic.html

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