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Classifying Arguments
Deductive (valid/invalid)
Inductive (strong/weak)
Arguments may be divided into two types:
in which the intention is certainty of the truth of the conclusion (and the logic can deliver)
in which the logic is limited to establishing the highest possible probability of the truth of the conclusion
Classifying Arguments
Why classify argument types?
To help develop a strategy for analysis
Should we be checking validity or strength?
Must every premise be acceptable for the argument to succeed?
To establish confidence expectations
Classifying Arguments
Deductive
If Franklin wanted a garden, he would have one.
If he had a garden, he would feel immense pride.
If he felt immense pride, he’d throw great parties.
So, if Franklin wanted a garden, he’d throw great parties.
(This example is a chain argument.)
Classifying Arguments
Deductive
If Franklin wanted a garden, he would have one.
If he had a garden, he would feel immense pride.
If he felt immense pride, he’d throw great parties.
So, if Franklin wanted a garden, he’d throw great parties.
Notice how the conclusion hides important connecting ideas.
Classifying Arguments
Deductive
A deductive argument aims at validity.
An argument is valid when the truth of the premises guarantees the truth of the conclusion.
Very important note: The truth of the conclusion of any argument does not logically guarantee the truth of the premises used to infer it.
Classifying Arguments
Deductive
All human beings are spiders.
All spiders are mammals.
Therefore, all human beings are mammals.
What can be said about this argument? Is it valid?
Classifying Arguments
Deductive
All human beings are spiders.
All spiders are mammals.
Therefore, all human beings are mammals.
The logic is valid and the conclusion is true, but those features alone obviously don’t guarantee the truth of the premises.
Classifying Arguments
Deductive
All human beings are mammals.
Therefore, if there is a human being in Chico, that person is a mammal.
This is a valid argument, because the truth of the lone premise guarantees the truth of the conclusion. In other words, if the premise is true, the conclusion must be true.
Classifying Arguments
DeductiveJefferson’s reasoning about the problem of social division:
Nature operates through mutual antagonisms.
Human beings are part of nature.
[Human beings cannot be removed from nature.]
So, the causes of factionalism cannot be removed.
The premises are true and the logic is valid.
Historical note--Jefferson’s question: Can anything then be done about the destructive effects of factionalism?
Classifying Arguments
DeductiveJefferson’s reasoning about the problem of social division:
Nature operates through mutual antagonisms.
Human beings are part of nature.
[Human beings cannot be removed from nature.]
So, the causes of factionalism cannot be removed.
Historical note--Jefferson’s solution: Government can be constructed to regulate the effects of the natural disagreements that occur among people.
Classifying Arguments
Deductive
The highest level of confidence is earned only by a sound argument.
A sound argument is a valid deduction whose premises are actually true.
Technically, we wouldn’t refer to what we believe to be a sound argument as a “strong” or even “very strong” argument, though in everyday conversation this terminology may serve the purposes of communication.
Classifying Arguments
???Individuals will be antagonistic toward each other when they perceive conflicting interests.
Individuals working individually cannot escape coming into conflict with others.
So, individuals organized into a rational society may escape some of the destructive effects of conflicts.
Is this conclusion justified by the premises?
Classifying Arguments
InductiveIndividuals will be antagonistic toward each other when they perceive conflicting interests.
Individuals working individually cannot escape coming into conflict with others.
So, individuals organized into a rational society may escape some of the destructive effects of conflicts.
Even with unstated “background knowledge” premises, this is a weak argument.
Classifying Arguments
InductiveWashington believed the United States should avoid foreign alliances whenever possible.
Canada is a foreign country.
So, Washington would have wanted the United States to avoid an alliance with Canada.
What separates this argument from the previous one?
Classifying Arguments
InductiveWashington believed the United States should avoid foreign alliances whenever possible.
Canada is a foreign country.
So, Washington would have wanted the United States to avoid an alliance with Canada.
At least in this argument, the premises are clearly relevant.
Classifying Arguments
InductiveMy car would accelerate from 0-60 in 5.5 seconds when I bought it.
My car would accelerate from 0-60 in 5.5 seconds a week ago.
So, my car will accelerate from 0-60 in 5.5 seconds today.
What level of confidence should one have here? Would it make much difference if we were driving in my car when I presented this argument?
Classifying Arguments
InductiveInductive arguments are never "valid." They are classed as
- Strong
- Weak
While validity is either proved or not, strength and weakness are less precise categorizations. Sufficient background knowledge and good judgment are important factors in evaluating inductive arguments.
Classifying Arguments
Inductive
Note on accepting inductive conclusions:
The conclusions of inductive arguments may be acceptable if they meet a minimum standard of the preponderance of the evidence.
In critical situations, the standard for acceptance may be much higher.
Classifying Arguments
Inductive
Note on inductive fallacies:
Inductive fallacies are patterns of inductive reasoning that are known to be deceptively weak.
They violate the rules of good argumentation by having premises that are either insufficiently probable or insufficiently relevant.
Classifying ArgumentsTwo inductive fallacies:Fallacy of Division
Inferring that what holds true of a group automatically holds true for all of the individuals in that group
Fallacy of Composition
Inferring that what holds true for individuals will automatically hold true for a group composed of those individuals
Classifying ArgumentsTwo inductive fallacies:Fallacy of Division
America is known for its historical commitment to freedom. So every American who plays a role in American history can be expected to have a commitment to freedom.
Fallacy of Composition
Communities of Muslims are cohesive and orderly. Communities of Jews are cohesive and orderly. So, a community composed of Muslims and Jews will be cohesive and orderly.
