Philosophy B7: Introduction to Logic
Instructor: McNellis
Identifying Type of Reasoning within an ArgumentDeductive or Inductive
Section 1.3
Terms: deductive, inductive
Forms of deductive arguments: arg’s based on math, definition, categorical syllogism, hypothetical syllogism, and disjunctive syllogism.
Forms of inductive arguments: arg’s from prediction, analogies, generalizations, authority, signs, and causal inference.
Notes: Distinguishing type of reasoning, i.e., between inductive and deductive, can be simplified by focusing on the various forms of arguments, as outlined in the “terms”.
Lecture Examples:
1. Look at these footprints in the mud by our home window. We must have a peeping tom.
2. The US Congress has more members than there are days in the year. Therefore, at least two members of Congress have the same birthday.
Exercise One: Identify deductive argument form
1. Joe is mendacious, therefore he lies a lot.
2. All men are mortal. Socrates is a man. Therefore Socrates is mortal
3. If it rains this morning, the grass will get wet. It rained this morning. Therefore the grass is wet.
4. Either Insider Trading is a not a crime or it is punishable by the state. Insider Trading is a crime. Therefore, it is punishable by the state
5. Because triangle A is congruent with triangle B, and triangle A is isosceles, it follows that triangle B is isosceles.
Exercise Two: Identify inductive argument form.
1. Because I bowled a 202 last week, therefore I will bowl at least a 200 this week.
2. This morning’s Bakersfield Californian has an article about Bakersfield College in its “Local” section, therefore the New York Times probably has an article about BC too.
3. Both Emma and Allison have Ph.D’s in Philosophy. One then can assume both have read one of the most important philosophical works of the Modern period, Rene Descartes’ Meditations.
4. Driving along the freeway, Paul sees a sign that there is a serious curve ahead and speed limit is 35. Odds are that there really is a serious curve up ahead.
5. A bottle of Sprite was accidentally left in the freezer overnight. Therefore, it froze.
6. This piece of chicken is dry and crunchy, so it must have been overcooked.
7. Amoco, Exxon, and Texaco are all listed on the New York Stock Exchange (NYSE). It must be the case that all major American oil companies are listed on the NYSE.
8. Because Erin’s philosophy instructor said that the moon is made of cream cheese and that cottage cheese is purple, the moon must be made of cream cheese and the color of cottage cheese is purple. My goodness, what have I been thinking all these years!
Practice Exercise
1. If Alexander the Great died from typhoid fever, then he became infected in India. Alexander the Great did die from typhoid fever. Therefore, he became infected in India.
2. The rainfall in Seattle has been more than 15 inches every year for the past 30 years. Therefore, the rainfall next year will probably be more than 15 inches.