The document discusses deductive reasoning and deductive fallacies. It explains that a deductively valid argument is one where the premises cannot be true and the conclusion false without changing the meanings of terms or rules of grammar. Certain language configurations form valid argument templates. Reasoning can be done deductively about declarative statements, classes of objects, and relationships using templates like denial of the consequent. However, there are also fallacious templates that appear valid, such as affirming the consequent. Fallacies occur in reasoning about classes through mistakes like false classification or about relationships through errors like false identity. Precision is needed to avoid fallacies in one's own reasoning and when evaluating others' arguments.

1. Chapter 8
Evaluate Deductive
Reasoning and Spot
Deductive Fallacies

2. Deductive Validity and Language
• An argument is deductively valid if there is
no possibility, real or imaginable:
– Short of changing the very meanings of the
terms and the rules of grammar:
– That will make the premises all true and the
conclusion false
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3. Deductive Validity and Language
• Certain configurations of language form
deductively valid argument templates
• Without violating the meanings of the
words/grammatical rules of the language:
– There is no possible way for the premises all
to be true and the conclusion false
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4. Deductive Validity and Language
• Reasoning Deductively about Declarative
Statements
– Denying the Consequent
– Affirming the Antecedent
– Disjunctive Syllogism
– Neither, Unless, and Only
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5. Deductive Validity and Language
• Reasoning Deductively about Classes of
Objects
– Applying a Generalization
– Applying an Exception
– The Power of Only
• One of the most interesting words in the language:
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6. Deductive Validity and Language
– Only has the power to change the meaning of a
sentence depending on where it is placed
• Classes and Objects
• Reasoning Deductively about
Relationships
– Natural languages are rich with terms that
describe relationships
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7. Deductive Validity and Language
– Our understanding of the logical implications
of relational terms is part of:
• Our comprehension of language
– Transitivity, Reflexivity, and Identity
• Transitivity Relationship
• Reflexivity Relationship
• Identity Relationship
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11. Fallacies Masquerading as Valid
Deductive Arguments
• Just as there are valid argument
templates there are fallacious argument
templates
• Precision of thought and expression is the
key to avoiding these mistakes in:
– Our own argument making and also in our
evaluation of the arguments offered to us
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12. Fallacies Masquerading as Valid
Deductive Arguments
• Fallacies When Reasoning with
Declarative Statements
– Affirming the Consequent
– Denying the Antecedent
– The House M.D. Fallacy
• Fallacies When Reasoning about Classes
of Objects
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13. Fallacies Masquerading as Valid
Deductive Arguments
– There are logically correct ways of reasoning
about classes of objects & their members:
• There are familiar mistakes we often hear being
made
– False Classification
• Examples of False Classification seem remarkably
abundant
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14. Fallacies Masquerading as Valid
Deductive Arguments
– Fallacies of Composition and Division
• Reasoning about the relationships of parts and
wholes can appear to be deductively valid:
– But fail because the attribute that applies to the parts
may not apply to the whole, or vice versa
– Mistaken Identity
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15. Fallacies Masquerading as Valid
Deductive Arguments
• Fallacies that occur when reasoning about
relationships like identity, reflexivity, or transitivity:
– Most often occur when people think they are talking
about the same thing, but in fact are not
– False Reference
– Create Your Own Deductive Reasoning
Examples
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