# LOGIC

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```					LOGIC

DEDUCTIVE
Vs
INDUCTIVE
DEDUCTIVE REASONING
• 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: Deduction deals more with soundness of
arguments than "truth".
• Given that their premises are true, the conclusions of deductive
reasoning must be true.
• For instance, if it is true that all dogs are animals, and if it is true
that all animals are living things, then it must be true that all dogs
are living things
• Effort in deduction is spent in determining
whether arguments are sound.
• Many puzzles involve deductive reasoning.
• Solve this puzzle below. Explain your
solutions.?
• a) You are marooned on an island, where
there are only liars and truth-tellers. You
meet a couple and the husband says, "My wife
told me that she is a liar.". Is he a liar or a
truth-teller?
• A liar of course. No one on the island can
claim themselves to be a liar - if they are
truth-tellers, it would be a lie, and they
cannot lie; conversely, if they are liars, it
• A liAr becAuse…if his wife wAs A liAr then
she would have told her husband she was a
truth-teller.
• If his wife was a truth-teller she would have
told her husband she was a truth-teller.
• If the first had happened and the man was a
truth teller, he would have told you she was
a truth teller.
• If the second had happened and the man was
a truth teller, he would have told you she
was a truth teller.
• If the first had happened and the man was a
liar, he would have told you she was a truth
teller.
• And ditto if the second had happened and the
INDUCTIVE 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, by its very nature, is more open-ended and
exploratory, especially at the beginning.
“NEVER ASSUME ANYTHING…BEWARE OF FAULTY BELIEFS
BUILT ON THE SHAKY GROUND OF FAULTY PERCEPTIONS”

• Francis Bacon …science should be used to explAin the
world and the universe.
• And, religion should explain faith.
• Bacon advocated the SCIENTIFIC METHOD OF REASONING
(inductive reAsoning…inductive reAsoning is Also
called scientific reasoning)
• LOGIC…the wAy we think…hAs been divided into two
forms of reasoning INDUCTIVE AND DEDUCTIVE
REASONING.
• Inductive reasoning essentially involves
generalization.
• After observing a number of examples,
conclusions are drawn which seem most
likely.
Inductive reasoning…another example

• Honey bee hives are dying all across the country.
This is an actual fact. What is killing them?
• I observe that five hundred of these hives have
varroa mites. However, the other five hundred hives
do not have mites.
• I observe, in my very scientific way, that hives with
mites usually die in a year, but hives without mites
live.
• I conclude that varroa mites are killing honey bees.
• When an argument claims that the truth of its
premises make it likely or probable that its
conclusion is also true, it is said to involve inductive
reasoning.
• so, frAncis bAcon’s scientific Method involves
OBSERVATION, MEASUREMENT, EXPERIMENTATION,
HYPOTHESIS, AND VERIFICATION
• These two methods of reasoning have a very different "feel" to them
when you're conducting research.

• Inductive reasoning, by its very nature, is more open-ended and
exploratory, especially at the beginning.

• Deductive reasoning is more narrow in nature and is concerned with
testing or confirming hypotheses. Even though a particular study may
look like it's purely deductive (e.g., an experiment designed to test the
hypothesized effects of some treatment on some outcome), most social
research involves both inductive and deductive reasoning processes at
some time in the project.

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 views: 1 posted: 4/21/2012 language: English pages: 8