1.4 Validity, Truth,
Soundness, Strength and
Cogency
Goal: Learn the terms used to
evaluate inductive and deductive
arguments
Deductive Arguments
An argument in which it is claimed that it is
impossible for the conclusion to be false if
the premises are true is a deductive
argument.
That is, it is claimed that the argument it
valid.
In a valid argument, if the premises are true,
the conclusion must be true too.
“Validity” describes the relationship that
the premises bear to the conclusion in
a deductive argument.
The test for validity: Imagine that the
premises are true and the conclusion
is false
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
If you cannot imagine that the
premises are true and the conclusion
is false, then the argument is VALID.
If you can imagine that the premises
are true and the conclusion is false
then the argument is INVALID.
P1. All CCU students are hardworking.
P2. Howie is a CCU student.
C. So, Howie is hardworking.
Valid: if the premises were true, the
conclusion could not be false.
P1. All CCU students are hardworking.
P2. Howie is hardworking.
C. So, Howie is a CCU student.
Invalid: if the premises were true, the
conclusion could still be false.
In a “good” argument the premises
support the conclusion (validity) AND
the premises are true.
A “good” deductive argument is called a
“sound” argument. A sound argument
is valid and has all true premises.
P1. All CCU students are hardworking.
P2. Howie is a CCU student.
C. So, Howie is hardworking.
Valid: if the premises were true, the
conclusion could not be false.
False premise(s)
Unsound
Sound = Valid + True Premises
P1. If Obama is president then he is
Commander in Chief.
P2. Obama is president.
C. Therefore, he is Commander in Chief.
Is this argument sound?
Sound = Valid + True Premises
P1. All cats have tails.
P2. My dog has a tail.
C. So, my dog is a cat.
Is this argument sound?
Inductive Arguments
An argument in which it is claimed that it is
improbably that the conclusion is false if the
premises are true is an inductive argument.
That is, it is claimed that the argument is
strong.
A strong argument is one whose conclusion is
probably true given the truth of the
premises.
The test for strength: Imagine the
premises are true, and determine
whether the conclusion is probable
given the truth of the premises.
Does the truth of the premises make it
more like that the conclusion is true
then had the premises been false?
P1. All past presidents have been men.
C. The next president will be a man.
Inductive: Possible for the conclusion to
be false
Can be made stronger or weaker given
more information.
There are degrees of strength!
P1. All past presidents have been men.
C. The next president will be a man.
P1. All past presidents have been
women.
C. The next president will be a woman.
P1. Every student I know has a cell
phone.
C. So, all students have cell phones.
P1. Every only child surveyed reported
being satisfied not having siblings.
C. Thus all only children are so satisfied.
Cogent = Strong + True Premises
P1. I have lost every hand so far.
C. So, I will win the next hand.
P1. Korby Ray used Ultra 90 and lost
50#.
C. So, if I use Ultra 90 I will lose 50#.
Arguments = Premises + conclusions
Factual claim (are the premises true?)
Inferential claim (is the argument
valid/strong?)
Deductive Arguments
Sound = Valid + True premises
{valid: if the premises are true, the conclusion must be
true}
Inductive Arguments
Cogent = Strong + True Premises
{strong: the conclusion is probably true if the premises are
true}
Deductive Arguments
1. All hamburgers are high in fat.
Quarter-pounders with cheese are
hamburgers. Therefore, quarterpounders with cheese are high in fat.
Sound ___ = Valid ___ + True premises ___
Deductive Arguments
1. All hamburgers are high in fat.
Quarter-pounders with cheese are
hamburgers. Therefore, quarterpounders with cheese are high in fat.
Sound _  __ = Valid ___ + True premises _  *__
2. All hamburgers are high in fat.
Chicken nuggets are high in fat.
Therefore, chicken nuggets are
hamburgers.
Sound ___ = Valid ___ + True premises ___
2. All hamburgers are high in fat.
Chicken nuggets are high in fat.
Therefore, chicken nuggets are
hamburgers.
Sound _x__ = Valid __x_ + True premises _  __
3. All hamburgers are good sources of
vitamins. Fresh vegetables and fruit
are hamburgers. Therefore, fresh
vegetables and fruit are good sources
of vitamins.
Sound ___ = Valid ___ + True premises ___
3. All hamburgers are good sources of
vitamins. Fresh vegetables and fruit
are hamburgers. Therefore, fresh
vegetables and fruit are good sources
of vitamins.
Sound _x__ = Valid _  __ + True premises _x__
Inductive Arguments
1.
Meatpacking has become the most
hazardous occupation in the US, with
three times the injury rate of factory work.
Therefore, John who works at a
meatpacking plant will probably get
injured on the job.
Cogent___ = Strong ___ + True Premises ___
2. I haven’t gotten sick from eating fast
food yet, so I will probably get sick if I
eat fast food any time soon.
Cogent___ = Strong ___ + True Premises ___
3. McDs promises, “…to use only fresh,
wholesome ingredients when serving
you and your family;” so they only use
fresh, wholesome ingredients in their
food.
Cogent___ = Strong ___ + True Premises ___
4. Because McDs is the single largest
purchaser of US beef, they have
considerable say over how beef is
processed in this country. So, the beef
they buy (and sell) is safe.
Cogent___ = Strong ___ + True Premises ___
5. McD’s webpage has a statement from
Dr. Dean Ornish whose diet has been
proven to reduce heart disease;
therefore, the foods that McDs serves
are part of a heart-healthy diet.
Cogent___ = Strong ___ + True Premises ___