reasoning from inarguable premises the conclusion is unarguable if the syllogism is structured correctly Example Because Socrates is human he is mortal Major Premise All ID: 656416
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Slide1
syllogism – logical reasoning from inarguable premises; the conclusion is unarguable if the syllogism is structured correctly.
Example:
Because
Socrates is human,
he
is
mortal
.
Major
Premise: All
humans are mortal
(
irrefutable generalization)
Minor Premise:
Socrates
is a human
Conclusion:
Therefore
, Socrates is
mortalSlide2
enthymeme – logical reasoning with one premise left unstated; instead of having an irrefutable general truth for major premise, it is an assumption, statement, or proposition that the writer presumes and the audience accepts.
Example
:
[Because gravity exists,] my pencil will fall when I drop it.
[Major
Premise:
Gravity exists. (a theory)]
Minor Premise:
My pencil exists in gravity.
Conclusion:
Therefore
,
my pencil falls when I drop it.Slide3
faulty syllogism – when one or both of the premises are refutable or untrueMajor
Premise:
All women are wise. (refutable)
Minor Premise:
Ms. Wallingford is a woman.
Conclusion: Therefore, Ms. Wallingford is wise.
Major
Premise:
Poisonous snakes have spots.
Minor
Premise:
That snake has spots.
Conclusion:
Therefore
,
that snake is poisonous.Slide4
deductive reasoning – reasoning that begins with a general principle and concludes with a specific instance that demonstrates the general principle
commonly
associated with
“
formal logic
.”involves reasoning from known premises, or premises presumed to be true, to a certain conclusion.
the conclusions reached are certain, inevitable, inescapable.
Example of Deduction
major premise: All tortoises are vegetarians
minor premise: Bessie is a tortoise
conclusion: Therefore, Bessie is a vegetarian
Deductive reasoning is commonly found in the natural sciences or
“
hard
”
sciences, less so in everyday arguments
Occasionally, everyday arguments do involve deductive
reasoning:
Example
:
“
Two or more persons are required to drive in the diamond lane. You don
’
t have two or more persons. Therefore you may not drive in the diamond lane
”Slide5
inductive reasoning – reasoning that begins by citing a number of specific instances or examples and then shows how collectively they constitute a general principle
commonly known as
“
informal logic
,
” or “everyday argument”
involves drawing uncertain inferences, based on
probabilistic
reasoning.
the
conclusions
reached are probable, reasonable, plausible, believable
Example of Induction
Boss
to employee:
“
Biff has a tattoo of an anchor on his arm. He probably served in the Navy.
”
Inductive reasoning is found in the courtroom, the boardroom, the classroom, and throughout the media
Most, but not all everyday arguments are based on induction
Examples: The
“
reasonable person
”
standard in civil law, and the
“
beyond a reasonable doubt
”
standard in criminal
law