Logical Reasoning: Deduction vs. Induction - Understanding Basic Concepts

1. Chapter 3Basic Logical Concepts

2. Deduction vs. Induction • Deductive Arguments try to prove their conclusions with rigorous, inescapable logic. Example: • All humans are mortal. • Socrates is a human. • Therefore, Socrates is mortal. • Inductive Arguments try to show that their conclusion are plausible (likely or probable), given their premises: • So far, every class, the professor has worn a tie. • Therefore, next class, the professor will wear a tie.

3. True/False • Indicate in the space provided whether the following statements are true (T) of false (F). • _____ 1. If an argument contains the indicator words “probably” or “likely” it is probably an inductive argument. • _____ 2. Deductive arguments always proceed from the general to the particular. • _____ 3. A geometrical proof is an example of an inductive argument. • _____ 4. In a deductive argument the conclusion is claimed to follow necessarily from the premises. • _____ 5. No inductive argument provides logically conclusive support for its conclusion.

4. _____ 1. If an argument contains the indicator words “probably” or “likely” it is probably an inductive argument. • _____ 2. Deductive arguments always proceed from the general to the particular. • _____ 3. A geometrical proof is an example of an inductive argument. • _____ 4. In a deductive argument the conclusion is claimed to follow necessarily from the premises. • _____ 5. No inductive argument provides logically conclusive support for its conclusion. • 1. T • 2. F • 3. F • 4. T • 5. T

5. 1. Arguments that try to prove their conclusions with rigorous, inescapable logic are • a. logically reliable. • b. inductive. • c. abductive. • d. deductive. • 2. An argument in which the conclusion is claimed to follow probably from the premises is • a. implicative. • b. inductive. • c. deductive. • d. none of the above

6. 1. Arguments that try to prove their conclusions with rigorous, inescapable logic are • a. logically reliable. • b. inductive. • c. abductive. • d. deductive. • 2. An argument in which the conclusion is claimed to follow probably from the premises is • a. implicative. • b. inductive. • c. deductive. • d. none of the above • 1. d • 2. b

7. 3. Which of the following is not a common induction indicator word or phrase? • a. it logically follows that • b. likely • c. chances are that • d. none of the above • 4. If an argument contains the words “it must be the case that,” then it is certain that the argument is • a. inductive. • b. deductive. • c. logically reliable. • d. none of the above

8. 3. Which of the following is not a common induction indicator word or phrase? • a. it logically follows that • b. likely • c. chances are that • d. none of the above • 4. If an argument contains the words “it must be the case that,” then it is certain that the argument is • a. inductive. • b. deductive. • c. logically reliable. • d. none of the above • 3. a • 4. d

9. Distinguishing Deductive Arguments from Inductive Arguments • For each of the following arguments, indicate whether it is best interpreted as deductive (D) or inductive (I) by circling the appropriate letter. • 1. Most days in the year are weekdays (as opposed to weekends). There will come a day when a huge asteroid strikes the earth. Thus, the day a huge asteroid strikes the earth will likely be a weekday. (D/I) • 2.That Delbert Johnson is not a singer follows from the following facts: (a) all singers can carry a tune, and (b) Delbert Johnson cannot carry a tune. (D/I)

10. 1. Most days in the year are weekdays (as opposed to weekends). There will come a day when a huge asteroid strikes the earth. Thus, the day a huge asteroid strikes the earth will likely be a weekday. (D/I) • 2.That Delbert Johnson is not a singer follows from the following facts: (a) all singers can carry a tune, and (b) Delbert Johnson cannot carry a tune. (D/I) • 1. inductive • 2. deductive

11. 3. So far, no one has ever swum the Atlantic Ocean non-stop—or even come remotely close to doing so. It is unlikely in the extreme, therefore, that anyone taking this test will swim the Atlantic Ocean non-stop. (D/I) • 4. Dudley expects to get thirty miles to a gallon from the car he bought last week, but that’s crazy. The car is a 1975 Belchfire with twelve cylinders and a 480 horsepower engine, and it needs a tune-up. (D/I)

12. 3. So far, no one has ever swum the Atlantic Ocean non-stop—or even come remotely close to doing so. It is unlikely in the extreme, therefore, that anyone taking this test will swim the Atlantic Ocean non-stop. (D/I) • 4. Dudley expects to get thirty miles to a gallon from the car he bought last week, but that’s crazy. The car is a 1975 Belchfire with twelve cylinders and a 480 horsepower engine, and it needs a tune-up. (D/I) • 3. inductive • 4. inductive