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Medical Ethics
Darin Harootunian
9/12/11
2
We can identify deductively valid arguments simply by their
form
(at least in almost all cases).
W
e don’t need to consider the truth of
the premises to determine whether the argument is valid or invalid.
Here are some valid inference forms
that we’ll be
using this
semester:
Modus Ponens
1) If P, then Q.
2) P
Thus, 3) Q.
Modus Tollens
1) If P, then Q.
2) ~Q.
Thus, 3) ~P.
I’ll give you some o
ther valid inference when we come across them in the course
–
there are
many
.
For now
, let’s consider
two
invalid
arguments:
Argument G
1) If John is a cardiologist, then John is a medical doctor.
2) John is not a cardiologist.
Thus, 3) John is not a medical doctor.
Argument H
1) If John is a cardiologist, then John is a medical doctor.
2) John is medical doctor.
Thus, 3) John is a cardiologist.
Why
are these arguments invalid?
Think about it.
For an invalid argument, there is always a
counterexample
to it.
A
counterexample
is a scenario in which the premises of the
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 Fall '07
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