Transcript Inductive and Deductive Reasoning

Inductive and
Deductive Reasoning
AP Language and Composition

Deductive reasoning works from the more
general to the more specific. Sometimes this
is informally called a "top-down" approach.
We might begin with thinking up a theory
about our topic of interest. We then narrow
that down into more specific hypotheses that
we can test. We narrow down even further
when we collect observations to address the
hypotheses. This ultimately leads us to be
able to test the hypotheses with specific data
-- a confirmation (or not) of our original
theories.
Deductive Reasoning
 Theory
◦Hypothesis
Observation
◦Confirmation
Deductive Reasoning
Inductive reasoning works the other way, moving
from specific observations to broader generalizations
and theories.
 Informally, we sometimes call this a "bottom up"
approach (please note that it's "bottom up" and not
"bottoms up" which is the kind of thing the bartender
says to customers when he's trying to close for the
night!).
 In inductive reasoning, we begin with specific
observations and measures, begin to detect patterns
and regularities, formulate some tentative hypotheses
that we can explore, and finally end up developing
some general conclusions or theories.

Inductive Reasoning
Theory
◦Tentative Thesis
◦ Pattern
 Observation
Inductive Reasoning
Induction is usually described as moving
from the specific to the general, while
deduction begins with the general and
ends with the specific
 arguments based on experience or
observation are best expressed
inductively, while arguments based on
laws, rules, or other widely accepted
principles are best expressed deductively.

Induction vs. deduction
Adham: I've noticed previously that every time I kick
a ball up, it comes back down, so I guess this next
time when I kick it up, it will come back down, too.
 Rizik: That's Newton's Law. Everything that goes up
must come down. And so, if you kick the ball up, it
must come down.

◦ Adham is using inductive reasoning, arguing from
observation, while Rizik is using deductive reasoning,
arguing from the law of gravity.
◦ Rizik's argument is clearly from the general (the law of
gravity) to the specific (this kick)
 Adham's inductive argument, above, is supported by his
previous observations, while Rizik's deductive argument is
supported by his reference to the law of gravity.
 Thus, Adham could provide additional support by detailing those
observations, without any recourse to books or theories of
physics, while Rizik could provide additional support by
discussing Newton's law, even if Rizik himself had never seen a
ball kicked.
Examples
1. Which of the following claims would be
best expressed by inductive reasoning?
A. Your first quiz grade usually indicates
how you will do in the course.
B. The final exam accounts for 30% of the
course grade.
C. Late papers will not be accepted.
D. Gravity's Rainbow is required reading in
your course.

Exercises for Induction and
Deduction
2. Which of the following claims would be
best expressed by deductive reasoning?
a. California's population growth rate
slowed last year.
b. California residents appreciate their good
weather.
c. California residents are residents of the
United States.
d. More cars are registered in California
than in any other state.
3. Which of the following arguments would lead to a
deductive conclusion?
a. There was a mild winter this year, and previously
whenever there's been a mild winter the cherry crop
suffers.
b. The cherry crop needs at least a week of freezing
temperatures for best results, and this winter the
temperature stayed several degress above freezing.
c. Primo noticed that whenever the skiing was good in
the winter, the cherry crop was profitable, and this
year the skiing was good.
d. Not since 1972 have I seen a good cherry crop after
a mild winter, and this winter has been mild.
1.
A
It is much more likely that this claim
stems from personal observation than
from adherence to some general
principle, and so it would be best
expressed by an inductive argument.
Answers
2. C
Since California residents are residents of
the U.S. by definition, and definition is
one sort of general claim on which a
deductive argument can be based, this
claim would be best supported by a
deductive argument.
3. D
Though the premise about this year is
based on observation, the general or
"major" premise, "The cherry crop needs
at least a week of freezing temperatures,"
seems to be an assertion of established
principle, making this a deductive
argument with the conclusion, "The
results won't be best this year."
The difference between inductive and
deductive reasoning is mostly in the way
the arguments are expressed.
 Any inductive argument can also be
expressed deductively, and any
deductive argument can also be
expressed inductively.

Induction vs. deduction

Induction is the method of reaching a
potentially useful generalization
◦ People attending meetings after lunch are
invariably less attentive than those at morning
meetings

Deduction is the method of using such a
generality, now accepted as a fact
◦ Because we need an attentive audience, we
had better schedule the meeting at 10:30
rather than 1:00
Induction and Deduction
combined

A personnel manager may have
discovered over the years that electrical
engineering majors from Central College
are well trained in their field.
◦ His induction may have been based on records,
observations and opinions of people at his
company and perhaps he has made the usable
generalization about the training of Central
College electrical engineering majors.
Induction and Deduction
combined


He has received an application from a
graduate of Central college
His deductive process will probably work as
follows:
◦ Central college turns out well trained engineers
◦ The applicant was trained at central college
◦ Therefore the applicant must be well trained.

Syllogism
◦ Major premise
◦ Minor premise
◦ Conclusion
Induction and Deduction
combined

Create your own syllogism.
Syllogism

Patterns of Exposition p. 551.
Induction vs. Deduction

Do not use flimsy evidence
◦ Opinion, hearsay, or analogy that do not support a valid generalization


Don’t use too little evidence leading to a premature inductive leap
Don’t use misdirected appeals
◦ Misdirected Appeals
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Appeal to Authority, or Appeal to Questionable Authority
Appeal to Common Belief, or Appeal to Belief, Appeal to Popular Belief
Appeal to Common Practice, or Appeal to Tradition
Two Wrongs Make a Right
Appeal to Indirect Consequences, or Slippery Slope, Domino Theory
Appeal to Wishful Thinking
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Appeal
Appeal
Appeal
Appeal
Appeal
Appeal
◦ Emotional Appeals
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to
to
to
to
to
to
Fear, or Scare Tactics, Appeal to Force
Loyalty, or Peer Pressure, Bandwagon, Ad Populum
Pity, or Sob Story
Prejudice, or Appeal to Stereotypes
Spite, or Appeal to Hatred, Appeal to Indignation
Vanity, or Apple Polishing
http://www.funtrivia.com/playquiz/quiz2814762039ae8.html
Logical Fallacies