Chapter 3
Basic Logical Concepts
Deduction vs. Induction
•
Deductive Arguments try to prove their
conclusions with rigorous, inescapable logic.
Example:
1. All humans are mortal.
2. Socrates is a human.
3. Therefore, Socrates is mortal.
•
Inductive Arguments try to show that their
conclusion are plausible (likely or probable),
given their premises:
1. So far, every class, the professor has worn a tie.
2. Therefore, next class, the professor will wear a tie.
• 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.
• _____ 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
• 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. 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
• 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. 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
• 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)
• 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
• 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 nonstop. (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 tuneup. (D/I)
• 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