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Analyzing Arguments Workshop I
Ecological Agriculture Program
October 3, 2003
Chad Kruger
Introduction
When we hear an argument, the first thing we do is determine if we agree or disagree with the expressed opinion – ignoring the
merit of the argument itself.
Introduction
Examining the structure (and merit) of an argument can help us improve civic and
public dialogue on the issues that we face collectively as a society (such as agricultural structure, the use of
biotechnology, etc.).
Introduction
This first workshop on arguments will look at two basic structural forms of arguments
(deductive and inductive), noting common logical fallacies and providing opportunity to practice improving the structure of an
argument.
Introduction
This exercise is NOT DESIGNED AS AN OPPORTUNITY TO DEBATE OPINIONS – but rather to practice thinking critically
about the structure of arguments and ultimately improve your ability to share
your opinions “out there” in the “marketplace of ideas”.
Deductive Reasoning
Valid Argument
Two or more premises automatically lead to the conclusion.
Deductive Reasoning
Valid Argument
If the premises are true and the conclusion automatically follows from the premises
the argument is valid.
Deductive Reasoning
Valid Argument
• All vegetables are food
• A carrot is a vegetable
• A carrot is food
Deductive Reasoning
Invalid Argument
If even one premise is NOT true OR the conclusion does not automatically follow from the premises then the argument is
NOT valid
Deductive Reasoning
Invalid Argument
(false premise)
• All vegetables are food
• A strawberry is a vegetable
• A strawberry is food
Deductive Reasoning
Invalid Argument(false conclusion, conclusion does not follow
from premises)
• All vegetables are food• A carrot is a vegetable
• A carrot is a fruit
Deductive Reasoning
Structure of deductive arguments
Deductive arguments have a major premise (general assertion), a minor
premise (specific assertion) and a conclusion (derived from how the minor
premise relates to the major premise).
Deductive Reasoning
Structure of deductive arguments
• Major Premise All vegetables are food
• Minor Premise A carrot is a vegetable
• Conclusion A carrot is food
Deductive Reasoning
Sound arguments
We do not call deductive arguments true or false, we call them sound or unsound.
To be sound, the minor premise has to affirm the subject (antecedent) of the major premise or deny the predicate (consequent) of the major premise.
Deductive Reasoning
Sound arguments
(affirms the antecedent)All vegetables (antecedent) are food (consequent)
• A carrot is a vegetable • A carrot is food
(denies the consequent)Some vegetables (antecedent) are green (consequent)
• A carrot is a vegetable • A carrot is NOT green
• Some vegetables are NOT green
Common fallacies of deductive reasoning:
1) Affirming the consequent – The minor premise equates a specific instance to a consequent of the major premise.
• Eating vegetables improves your health.
• Strawberries improved my health.
• A strawberry is a vegetable.
Common fallacies of deductive reasoning:
2) Denying the antecedent – The minor premise equates that a specific instance is NOT an instance of the antecedent of the major premise.
• Eating vegetables improves your health.
• A strawberry is not a vegetable.
• Strawberries cannot improve your health.
Common fallacies of deductive reasoning:
3) Equivocation – changing the meaning of a word between premises or conclusions
• Using pesticides is a poor farming practice.
• Subsistence farmers are poor farmers.
• Subsistence farmers need training in agroecological systems.
Common fallacies of deductive reasoning:
4) Division – Attributes of a group (in the major premise) are applied incorrectly to an individual (in the minor premise).
• Birds are common in every area of the world.
• Spotted owls are birds.
• Spotted owls are common in every area of the world.
Inductive Reasoning
Inductive Argument
We use our knowledge and experience to reach conclusions based upon specific
observations.
Inductive Reasoning
Observation: John’s garden is very weedy.
Observation: I have not seen him much lately.
Prior experience: John usually takes care of the weeds.
Conclusion: John has been busy.
Inductive Reasoning
We do not call inductive arguments true or false, we call them strong or weak.
Common fallacies of inductive reasoning:
1) Hasty Generalization – Inductive leap based on insufficient information / observation.
• John’s garden is always weedy.
• John doesn’t care about his garden.
Common fallacies of inductive reasoning:
2) Exclusion – An important piece of information/observation is intentionally ignored.
• I ate strawberries from the garden last night and got a major stomachache. I can probably conclude that the strawberries were bad.
• I left out that I ate 5 pounds of strawberries.
Common fallacies of inductive reasoning:
3) False analogy – (Arguments from analogy are inductive) – similar to hasty generalization – a situation is compared to another when it is not sufficiently similar
• If you want to eat the best tasting apples, you should pick them in June. Apples and strawberries are both fruits and strawberries taste best in June.
Common fallacies of inductive reasoning:
4) Unrepresentative Sample – similar to exclusion – making an argument based upon data from a sample size not sufficient to represent the whole.
• A few students in our class told me that they are from family farms. Since this is a class about agriculture, most of the students must be from family farms.
Problem Sets:
• What are the problems of the following arguments?
• Is the argument a deductive argument or an inductive argument?
• Are there missing or assumed premises?• What fallacies have we committed? • How can we correct or improve these
arguments to make them valid, sound or strong?
Problem Sets:
Key to success: Whether you agree or disagree with the opinions expressed in the argument, you need to set them aside in order to rigorously examine
the merit of the argument’s structure.
Problem Sets:
The “Great Leap Forward” was the Chinese Communist Party’s economic plan for
growth and development of the Chinese economy between 1959 and 1962. The commune was the Party’s “vehicle” for
agricultural development. Communes failed to meet production goals of the Great Leap Forward and more than 30 million Chinese peasants died in the famines between 1959 and 1962. Communism is a bad economic
system for agricultural development.
Problem Sets:
Major Premise: The “Great Leap Forward” was the Chinese Communist Party’s economic plan for growth and development of the Chinese economy between 1959 and 1962.
Minor Premise 1: The commune was the Party’s “vehicle” for agricultural development.
Minor Premise 2: Communes failed to meet production goals of the Great Leap Forward
Minor Premise 3: more than 30 million Chinese peasants died in the famines between 1959 and 1962.
Conclusion: Communism is a bad economic system for agricultural development.
Problem Sets:
Is this a valid argument? NO.
The premises are “true”.
The conclusion is arguably true or false.
But, the conclusion does not follow from the premises.
Problem Sets:
The US agricultural system is based on capitalism. The US agricultural system is
wrought with social and ecological problems, such as heavy public subsidies, factory farms, genetic manipulation, soil
loss and fossil fuel consumption. Capitalism has corrupted the US
agricultural system.
Problem Sets:
Major Premise: The US agricultural system is based on capitalism.
Minor Premise: The US agricultural system is wrought with social and ecological problems.
Conclusion: Capitalism has corrupted the US agricultural system.
Problem Sets:
Is this a deductive or inductive argument?
If it is a deductive argument, is it valid or invalid, sound or unsound?
If it is an inductive argument, what fallacy does it commit?
Hasty Generalization?
Exclusion?
Problem Sets:
Native Americans lived sustainably (off the land) in a subsistence economy in North American for
several thousand years before European settlers arrived. John Jeavon’s “biointensive” research shows that the entire dietary needs of an adult
human can be grown on 1000 square feet of soil and that the entire needs of a family of four can be met through production from one acre. People who
produce their own food are not dependent on global consolidated food corporations, do not
contribute to the extensive environmental degradation of modern commercial agriculture and are healthier. A subsistence agricultural economy
is the best option for America.
Problem Sets:
Major Premise(s) / (Observations): People who produce their own food are not dependent on global consolidated food corporations, do not contribute to the extensive environmental degradation of modern commercial agriculture and are healthier.
Assumption (missing): Consolidation, environmental degradation and poor health are bad for people
Minor Premise (supporting detail): Native Americans lived sustainably (off the land) in a subsistence economy in North American for several thousand years before European settlers arrived.
Supporting detail (not a premise!): John Jeavon’s “biointensive” research shows that the entire dietary needs of an adult human can be grown on 1000 square feet of soil and that the entire needs of a family of four can be met through production from one acre.
Conclusion: A subsistence agricultural economy is the best option for America.
Problem Sets:
Is this a deductive or inductive argument?
If it is a deductive argument, is it valid or invalid, sound or unsound?
If it is an inductive argument, what fallacy does it commit?
Hasty Generalization?
False Analogy?
Unrepresentative Sample?
Problem Sets:
For your “microtheme” writing assignment, review an article
provided for you. Determine what are the premises and conclusions and
supporting data. Determine whether it is a deductive or inductive argument, whether it is valid, sound or strong,
and what fallacies the writer may commit. Also comment to how the
argument could be improved.
