PHIL 210 Study Guide - Quiz Guide: Deductive Reasoning, Modus Ponens
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4 Jun 2020
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PHIL 210-Critical Thinking
Book Notes
Chapter 1 The parts of public thinking deductive argument
Study notes 5
➢ Addition
o 1. P
▪ Therefore,
o 2. P or Q.
➢ Ex:
o 1. Foxes are mammals.
▪ Therefore,
o 2. Either foxes are mammals or crows are mammals.
➢ Ex2:
o 1. Foxes are mammals.
▪ Therefore,
o 2. Either foxes are mammals or lizards are mammals
➢ Doesn’t matter is statement adding “or” (Q) is true or false, requires at least one substatement
to be true. If we know that P is true than is garantees that P or Q is true, no matter what Q.
➢ Hypothetical Syllogism
o 1. If P Then Q
o 2. If Q Then R
▪ Therefore,
o 3. If P Then R.
➢ Ex:
o 1. If the dollar is devalued, then export will rise.
o 2. If exports rise, then unemployment will fall.
▪ Therefore,
o 3. If the dollar is devalued, unemployment will fall.
➢ Constructive Dilemma
o 1. P or Q
o 2. If P then R
o 3. If Q then S
▪ Therefore,
o 4. R or S.
➢ Ex:
o 1. Either it will snow tomorrow or there will be a quiz in class.
o 2. If it snows tomorrow, classes will be classed.
o 3. If there’s a quiz in class tomorrow, then ill fail it.
▪ Therefore
o 4. Either class will be cancelled tomorrow or I will fail a quiz tomorrow.
Other Structural Properties of Arguments
Linked arguments