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Lecture 6

PHI 1101 Lecture Notes - Lecture 6: Modus Ponens, Thanetian, Modus Tollens


Department
Philosophy
Course Code
PHI 1101
Professor
Mark Brown
Lecture
6

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Deductive Arguments:
An argument intended to provide logically conclusive support for its conclusion
The defining characteristic of a deductive argument is that it is valid or invalid
A deductive argument is intended to provide conclusive support for its
conclusion.
Final, definitive, undeniable support
The structure of some arguments is deductive
When arguments structured this way are good, they guarantee their
conclusion
In each case, if the premise offered really are true, then the conclusion must also be
true, and we can therefore describe that the argument as being valid.
Note: you have to look as the structure of the argument
Accordingly, if an argument has a combination of false premises and a false conclusion,
it is still valid.
Arguments that are valid can be described as having:
False premise and false conclusion
False premise and true conclusion
True conclusion and true conclusion
If an argument has a true premise and a false conclusion then it is invalid.
Chapter 3, Page 33
2. invalid
12. invalid
20. valid
Sentential Form
Conjunction (‘and’) =
P Q
Disjunction (‘or’) = v
P v Q
Negation (‘not’) = ~
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