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REASONING &
ARGUMENTS
Chapter 1 page 27 ff.
What is an argument?
 http://www.youtube.com/watch?v=kQFKtI6gn9Y
 “An argument is a connected series of statements to
establish a definite proposition”
 When trying to persuade  USE AN ARGUMENT
 Giving reasons to support a conclusion
 Parts of an argument:
 PREMISES: propositions taken as support or proof
 CONCLUSION: the proposition being proven or
supported
Consider this example
Capital punishment should not be used because wrongly convicted people will be
executed by mistake and this is totally unacceptable.
(What is the conclusion? What are the supports?)
P1
If capital punishment is used, then wrongly convicted people will be executed
by mistake.
P2
The execution of wrongly convicted people is totally unacceptable.
C
Capital punishment should not be used.
(P = premise, C = conclusion)
Conclusion-Indicators & Premise-Indicators
Conclusion-indicators
Premise-indicators
 Therefore
 Since
 Hence
 Because
 Thus
 Given that
 So
 Assuming that
 Consequently
 Inasmuch as
 It follows that
 For the reason that
 We may infer that
 We may conclude that
Deductive Arguments
 A DEDUCTIVE argument is either valid or invalid
 VALID deductive argument
 The conclusion is logically entailed in, or necessarily follows from the premises
 (the form of the argument “works” the conclusion follows the premises.
 THERE IS INFERENCE: the conclusion is CONNECTED to the premises)
 LOGICAL ENTAILMENT:
 Occurs when the conclusion must be true given that the premises are true.
 INVALID deductive argument
 An argument is offered as valid, but the conclusion is not logically entailed in the
premises.
 An argument could have true premises, and yet the conclusion is false
 (there is NO INFERENCE: the conclusion is NOT CONNECTED to the premises)
Deductive Reasoning
 Begins with a UNIVERSAL rule, truth, or generalize
statement.
 Leads to a particular/specific instance of the universal rule.
 In valid deductive reasoning / arguments, therefore, the
conclusions are NECESSARILY, DEFINITELY OR CERTAIN as
true.
 All men are mortal.
 Socrates is a man.
 Socrates is mortal.
Inductive Arguments
An argument where the conclusion is
PROBABLY true.
(Inductive reasoning proceeds from
specific / particular instances to develop
a generalization or “universal” rule)
It’s likely more helpful to judge inductive
arguments as strong or weak (not valid or
invalid)
Inductive Arguments
The basic assumption: present and past
observations lead to a general statement,
and will continue to follow that pattern in
the future.
Notice: since we haven’t observed ALL the
possibilities, our “rule” is only PROBABLE
(Consider David Hume…p. 32)
Abductive Arguments
Arguments where the conclusion is a “best
guess” that is to be judged to the most
plausible explanation among competing
alternatives, given that the premises are true.
The term, “abductive” comes from Charles
Sanders Pierce (19th C. American philosopher)
Comparing the Three
Deductive
If premises true 
conclusion true
Impossible for all premises
to be true & conclusion
false
Contradictory for premises
to be true and conclusion
false
If conclusion false, at least
one of the premises must be
false
Inductive
Abductive
If premises true 
conclusions probably
true
If premises true 
conclusion judged a
good candidate,
among other
possibilities, for
being true
unlikely that if
premises are true,
conclusion false
conclusion can be
false while all
premises true
Ockham’s razor the
basic assumption
conclusion can be
false while premises
true
Reasoning & Bias
 Francis Bacon (1561-1626)
 Focused on the utility of scientific knowledge for enabling
us to know better
 Novum Organon (New Instrument) departure from
Aristotle’s Organon
 Bacon: emphasized observation and induction
 Aristotle: preferred deduction, knowledge for its own sake
(not utility)
Idols of the Mind
 We strive to be impartial, objective & open-minded
 But, we can be swayed from reasoning clearly & correctly by
distortions
 Bacon called these distortions IDOLS, i.e., “revered false
appearances”
 Idols of:
 The tribe
 The cave
 The marketplace
 The Theatre
Idols of the Tribe
Biases common to all people that “are inherent
in human nature and the very tribe or race of
men, for man’s sense is falsely asserted to be
the standard of things.”
Human understanding like a false mirror
We should be wary of our sense perception for
our senses often deceive us.
Idols of the Cave
“Everyone has a cave or den of his own, which
refracts and discolours the light of nature,
owing either to his own proper and peculiar
nature, or his education…
Individual habits of thought, personal
experiences, & our own education, interests
The distortion is peculiar to each individual
person
Idols of the Marketplace
 Our thoughts are traded by the use of words in a
conversational marketplace
 The idols of the marketplace: sloppy use of words,
 i.e., words that are ill-defined, ambiguous
 “the ill and unfit choice of words wonderfully
obstructs the understanding.”
Idols of the Theatre
 Bacon cautions against blind acceptance of established
systems of knowledge,
 Like theatrical productions that present mere fiction
 We need to critically examine the foundations of our
philosophical, scientific, theological systems
 Uncritical acceptance of systems of thought: idols of the
theatre
Consider these distortions:
 Stereotyping other people & cultures
 Self-centred thinking, our own interests colour our
interpretations
 Peer pressure, pressure for social conformity, we have a
powerful psychological need to be liked & accepted by
others
 Confirmation bias, the tendency to accept information that
confirms what we already think and disregard information
that threatens not to confirm what we already think