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PHI 1101 Study Guide - Midterm Guide: Classical Logic

Course Code
PHI 1101
Laura Byrne
Study Guide

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Tuesday, September 13, 2016
Unit 1: Part 1 - Basic concepts
Definition: A kind of sentence used to make a claim, capable of being true or false
Most basic concept of critical thinking
Logic also calls them assertions or propositions
Property of being either true or false distinguishes them from sentences (is a type of
concept — statement
property — true or false
Logically Strong (inductively strong; deductively valid)
Logically Weak (Inductively Weak; Deductively valid)
Laws of Logic
Law of excluded middle/bivalence: Every statement must either be true or false (nothing in
the middle).
Bivalent = only 2 values (true & false)
classical logic (this) ex: Jane is pregnant - she either is or she isn’t
non-classical ex: Jane is dead - vampire or zombie?? lmao
It follows from this law that for any given proposition and its negation, one must be true and
the other one false. If a pro positing is true, negation must be false. (vice versa)
ex: Socrates is a man (true)
Socrates is not a man (has to be false)
Law of non-contradiction: It is impossible for a statement and its negation to be true at the
same time (you can’t truthfully assert or deny that something is the case)
ex: Lassie is a dog (true)
Lassie is brave (true)
Sets of Propositions
Propositions can be combined in groups or sets
Examples: Socrates is mortal. - assertion/proposition
Socrates is a philosopher - negation
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