PHIL 150 Chapter Notes - Chapter 1, F-H: Confidence Trick, Logical Reasoning, False Premise
10 May 2018
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PHIL Logic (R) Chapter 1 (F-H) What Logic Studies
Wireless Philosophy (Truth, Validity, Implicit, Soundness)
F. Deductive Arguments: Validity and Soundness
Logical analysis of a deductive argument: Assuming the premises are true, is it possible for the
conclusion to be false?
Valid deductive argument – Assuming the premises are true, it is IMPOSSIBLE for the conclusion
to be false (conclusion follows necessarily from the premises)
Invalid deductive argument – Assuming the premises are true, it is POSSIBLE for the conclusion
to be false (conclusion does not follow necessarily from the premises)
Determining whether a deductive argument is valid or invalid depends on logical analysis
Sound argument – A deductive argument is sound when the argument is valid and the premises
are true
o Every sound argument’s conclusion is true
Unsound argument – A deductive argument is unsound when the argument is invalid or if at least
one of the premises is false
Determining whether a deductive argument is sound or unsound depends on both logical analysis
and truth value analysis
Argument form – In categorical logic, an argument form is an arrangement of logical vocabulary
and letters that stand for class terms such that a uniform substitution of class terms for the letters
results in an argument
o An argument is valid or invalid based on its logical form, not its content
Statement form – In categorical logic, a statement form is an arrangement of logical vocabulary
and letters that stand for class terms such that a uniform substitution of class terms for the letters
results in a statement.
Ex: All dogs are cats. All cats are snakes. Therefore, all dogs are snakes.
o D = dogs; C = cats; S = snakes
o Statement form: All D are C.
o Argument form:
All D are C.
All C are S.
All D are S.
Substitution instance
o In categorical logic, a substitution instance of a statement occurs when a uniform
substitution of class terms for the letters results in a statement
o A substitution instance of an argument occurs when a uniform substitution of class terms
for the letters results in an argument
In a valid argument, it is impossible for the argument form to have true premises and a false
conclusion after conducting substitution instances, while in invalid argument forms, it is possible
to get a false conclusion from true premises
Counterexample
o Counterexample to a statement is evidence that shows the statement is false
o Counterexample to an argument shows the possibility that premises assumed to be true do
not make the conclusion necessarily true
o A single counterexample to a deductive argument is enough to show that the argument is
invalid
Ex: To show a deductive argument is invalid with counterexample
o All bomohs are scam artists.
All grifters are scam artists.
All bomohs are grifters.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Phil logic (r) chapter 1 (f-h) what logic studies. Wireless philosophy (truth, validity, implicit, soundness: deductive arguments: validity and soundness. Determining whether a deductive argument is valid or invalid depends on logical analysis: every sound argument"s conclusion is true. Valid deductive argument assuming the premises are true, it is impossible for the conclusion. Invalid deductive argument assuming the premises are true, it is possible for the conclusion. Sound argument a deductive argument is sound when the argument is valid and the premises. Unsound argument a deductive argument is unsound when the argument is invalid or if at least. Argument form in categorical logic, an argument form is an arrangement of logical vocabulary. Statement form in categorical logic, a statement form is an arrangement of logical vocabulary and letters that stand for class terms such that a uniform substitution of class terms for the letters results in an argument.
