ways of knowing: reason reason. cogito ergo sum reasoning deductive inductive
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Ways of Knowing: Reason
Cogito ergo sum
Deductive Reasoning: Syllogism
All men are mortal Socrates is a manTherefore Socrates is mortal
All blims are blamsSome blims are blomsTherefore some blams are bloms
- if the premises are valid- and the argument is valid- then the conclusion is valid
All panthers are pinkChe Guevara is a pantherTherefore Che Guevara is pink
Deduction and induction compared
Reasoning from general to particular
Reasoning from particular to general
All metal expand when heated.
A is a metal
Therefore A expands when heated
Metal A expands when heated;
metal B expands when heated;
metal C expands when heated.
Therefore all metals expand when heated.
More certain, but less informative than induction
More informative, but less certain than deduction.
The Bases of Reason: The Laws of Thought1 The law of identity: Whatever is, is2 The law of contradiction: Nothing can both be and not be3 The law of excluded middle: Everything must either be or not be
a priori knowledge
The Value of Reasonrationalism- Philos. The doctrine or theory that emphasizes the role of reason in knowledge, or claims that reason rather than sense experience is the foundation of certainty in knowledge. Freq. contrasted with empiricism. (OED)
The Limits of Reason: The Cretan Paradox
All Cretans are liarsI am a CretanTherefore I am a liar
Can reason be doubted?It is an act of faith to assert that our thoughts have any relation to reality at all- G K Chesterton
Can reason be doubted?The law of excluded middle is true when precise symbols are employed, but it is not true when symbols are vague, as, in fact all symbols are- Bertrand Russell
Can reason be doubted?You can never step into the same river twice- Heraclitus