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Midterm

PHI 1101 Study Guide - Midterm Guide: Lassi, Inductive Reasoning, Enthymeme


Department
Philosophy
Course Code
PHI 1101
Professor
Laura Byrne
Study Guide
Midterm

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Tuesday, September 20, 2016
Reasoning and critical thinking part 2
Arguments
The concept of an inference takes us to the concept of an argument
Arguments: a set of statements that claims that one or more of those statements, called the
premises, support, or justify, or make it reasonable to believe that another of those
statements, the conclusion, is true.
Standard form: to write an argument in standard form, we line up the premises, draw a line
under the last premise, then write the conclusion
Ex: All men are mortal.
Socrates is a man.
Socrates is mortal.
Logical Strength
We do not simply wish to argue, we wish to argue well.
What makes a good argument?
This brings us to another key concept — logical strength
This is a property of arguments
Arguments:
Concept — Argument
Property 1 — Logically strong or Logically weak
An argument always involves the claim that its premises support its conclusion.
But do they? Do the premises really support the conclusion?
When the premises really do support the conclusion, the argument is logically strong
When they do not really support the conclusion, the argument is logically weak
Logical Strength: An argument has logical strength when the premises, if true, actually
provide support for, justify, or make it reasonable to believe the conclusion is true
logically strong ex: If Lassie loves Timmy, then he will always protect him.
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Tuesday, September 20, 2016
Lassie loves Timmy.
Therefore Lassie will always protect Timmy.
logically weak ex: Sally has brown hair.
Therefore Sally is a poor student.
Features of Logical Strength
Feature 1
Notice: logically strong: the premises, if true, support the truth of the conclusion, or make it
reasonable to believe the conclusion is true
This does not mean the premises actually are true
It is possible for a logically strong argument to have false premises
logically strong w false premises ex: All men are immortal (false)
Lassie is a man (false)
Therefore Lassie is immortal.
logically strong w true premises: logically strong w false premises:
All men are mortal All men are immortal
Socrates is a man Lassie is a man
Therefore Socrates is mortal Therefore Lassie is immortal
**even though one is true and one is false arguments are of the same form.
Soundness
This is an additional property of arguments and a means by which we can assess them
Logical strength: if the premises are true, they support the truth of the conclusion or make it
reasonable to believe the conclusion is true
When an argument is logically strong and its premises actually are true, then we say it is
sound.
Definition: an argument is sound if it is logically strong and it has true premises
Deductive and Inductive Arguments
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