Inductive Logic. Induction is the process of drawing a general conclusion from incomplete evidence.

Transcription

1 Inductive Logic Induction is the process of drawing a general conclusion from incomplete evidence. An inductive leap is the intellectual movement from limited facts to a general conviction. The reliability of your conclusion depends on the quantity and quality of your observations.

2 Sample Sample- the limited facts that you have. The sample must be... Known Sufficient Representative

3 Sample Known? Is the sample known? Does the sample lack evidence - UFOs, Big Foot, Atlantis, or other extravagant claims point to conclusive evidence that is unavailable. If the sample is absent or unknown, you cannot reach a logical conclusion.

4 Do you have enough? Is the sample sufficient? Using too little of a sample to reach a broad conclusion is stereotyping. This can lead to an inductive leap that is not warranted. Be suspicious of the words typical or average. Joe and Sue did not finish their papers; therefore, my students are all lazy (two out of 76 is too small)

5 IS the sample Typical? Is the sample representative? A sample is unrepresentative when it is not typical of the whole class of things being studied. Watch for isolated statistics - Fox News Poll shows that 88% disapprove of Obamacare (100% of the audience is conservative). Any poll with a selective sample is unrepresentative (a web based poll only represents those who have visited that page and have responded to the poll)

6 Occam s Razor Occam s Razor When a body of evidence exists, the simplest conclusion that expresses all of it is probably the best. Remember that the person with the motive and opportunity and gun is probably guilty.

7 Deductive Reasoning Deductive reasoning moves from a generalization to a conclusion. Deductive form is often stated with a major premise, a minor premise and a conclusion. This argument in three parts is called a syllogism. Major premise: all humans are mortal. Minor premise: Socrates is a human. Conclusion: Socrates is mortal. All A is B; All B is C; therefore all A is C.

8 Reliable deductive argument For deductive argument to be reliable, the premises must all be true. The Major premise is derived from inductive reasoning; it is a general statement drawn from facts. To test the reliability, determine if the facts are known, sufficient and representative.

9 Example Major premise: All cows are purple. {Unproven} Minor premise: Betsy is a cow. Conclusion: Therefore, Betsy is purple. The form is correct, but the major premise is incorrect.

10 Ambiguous language For deductive argument to be reliable, the language must be unambiguous. Major premise: Killing an innocent human being is murder. (surgery; cell ) Minor premise: Abortion kills an innocent human being. Conclusion: Abortion is murder. When can the embryo survive outside of the womb? When does it have consciousness?

11 Defined terms Marriage is a religious ceremony that unites a man and a women as one. Sue and Jane are women going in front of a judge. Therefore, Sue and Jane cannot be married. How do we define Marriage? Religious or civil?

12 Example Deduction Deductive reasoning must have a valid form. Major premise: All murderers have ears. Minor premise: All Methodists have ears. Conclusion: All Methodists are murderers. Here a key element is left out of the minor premise (murder).

13 Support Supporting the position (offer reasons to accept it). See pp. 277 in the text FACTS: STATEMENTS THAT CAN OBJECTIVELY BE PROVEN TRUE MAKE SURE THAT YOU THESE ARE FROM TRUSTWORTHY SOURCES Statistics: these are sometimes mistaken for facts; however, they are not facts. Stats are numerical data based on interpretations. Who interprets the numbers and how the interpretations are conducted will affect reliability (not all stats are found logically or scientifically).

14 Support Examples and anecdotes: illustrations must be representative in order to support your claim. Anecdotes are brief narratives. Often, examples and anecdotes are added for emotional appeal (pathos). They tend to make truth claims, but are more like vivid images than logical appeals (add other support to reinforce your illustrations).

15 Support Quotes from experts (expert testimony): these strengthen your viewpoint if the sources are credible. Try to find unbiased sources; do not assume that your audience is ignorant they know that some sources are influenced by money or politics. Even if your source clearly takes one side, he should show knowledge of the entire issue. Doctors from major universities trump unnamed online sources. Make sure the source is truly an expert in the area of study. Sources can be primary (right there), secondary (has studied many right there sources), or tertiary (on the outside looking into the issue but has never been right there nor immersed in the study per se third level). Unfortunately, most journalists, online sources, etc. are tertiary.

16 Support Analogies: these are comparisons; they claim two unlike things have one or common characteristic. They can be clever and emotionally persuasive; however, no two things are exactly alike the opposition may point this out. Still, use analogies to complement other support. Examples: Drug use is a matter of behavior control. It's like overeating or gambling. It would be ridiculous to declare war on overeating, so it's ridiculous to declare war on drugs. The war on drugs is like any war. We will not begin to win until we begin to shoot drug dealers on sight.