PHI 1101 Lecture Notes - Lecture 2: Principle Of Bivalence

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11 Aug 2016
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Lecture 2 - Two laws of Logic
Two Laws of Logic
This property of being either true or false brings us to two fundamental
laws of Logic.
1. The Law of Non-Contradiction
2. The Law of the Excluded Middle or the Law of Bivalence
Example: Socrates is a man - Proposition
Socrates is not a man - Negation of that proposition
For the sake of clarity and brevity, logicians and philosophers
sometimes like to represent statements with symbols, or refer to them in
a short hand way
They find if very convenient to represent statements with lower case
letters like a, b, c or p, q, r
Negation
Socrates is a man. - p
Socrates is not a man. not-p (can also be written -p)
Lassie is a dog. - p
Lassie is not a dog. - not-p
Example:
Student: Professor, did I pass the test?
Professor: Yes you did pass the test.
Student: I passed the test?
Professor: No, you did not pass the test.
Student: ????
Professor: You did pass the test, and you did not pass the test.
Using a p and a not-p at the same time..in the same respect
Sucks out enough content to dissipate
The Law of Non-Contradiction
The sentences we are dealing with obey what is known as the Law of
Non-Contradiction.
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