5. Deductive Argument
Major Premise:
If the stars look “washed” at
night, it will most likely be
cloudy in the morning.
Minor Premise:
The stars look “washed”
tonight.
Conclusion:
It will most likely be cloudy
in the morning.
It will be clear
tomorrow
The sky is so clear,
it looks like the
stars are freshly
washed.
It is actually
cloudy in the
morning
Washed stars =
cloudy morning
Observe this on
many occasions
(at least 10 in
this case)
6. Inductive Deductive
• Note that it is not the initial observation that leads to the general law
that becomes the major premise, but rather the number of times that
same observation is made that leads me to believe in the final
conclusion, which then becomes the general law.
7. Inductive Deductive
• Note that it is not the initial observation that leads to the general law
that becomes the major premise, but rather the number of times that
same observation is made that leads me to believe in the final
conclusion, which then becomes the general law.
• Note that I had to say “most likely” because inductive reasoning deals
with probabilities. An inductive conclusion can almost never be
“proven” to be correct. It can be proven incorrect, but otherwise, we
simply accept it based on probability, until something comes along
that explains the observations better.
8. Deductive Argument
Major Premise: All Joes are
jerks
Minor Premise:
This guy’s name is Joe
Conclusion:
He will be a jerk
Reality: This Joe is not a jerk
Modus Tollens: I have
denied the consequent;
therefore my major premise
cannot be true.
Hypothesis: All
Joes are jerks
One boyfriend
named Joe is a
jerk
Another boyfriend
named Joe is a
jerk. I meet a
Joe who
is not a
jerk
9. Scientific method finds bad logic
• I have disproven my inductive hypothesis; therefore, by deductive
logic, it CANNOT be true.
Hypothesis: All
Joes are jerks
