March 13th Lecture.docx

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22 Apr 2012

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March 13th Lecture - Reasoning (Continued)
Formal reasoning
Deductive reasoning
1. Conditional:
Modus ponens (affirm antecedent)
Modus tollens (deny consequent) - proved by contradiction - people don't usually test
for this
Cosmides and Tooby: domain-specific neural system for detecting breaches of social
e.g. drinking and driving is a breach of social contract
We can apply our reasoning abilities quickly and without biases
Evolutionarily advantageous - we want to quickly identify who is stealing our
food, etc.
Maybe this problem is easier because it is easier for us to understand because it
is a real life example
**read box, not in main reading
2. Syllogistic: drawing conclusions from two premises - don't have to be true, just
logically plausible
Linear syllogisms
The relationship b/w the terms is linear, involving a quantitative or
qualitative comparison in which each term shows more or less of a
particular attribute
e.g. you are smarter than your best friend, your best friend is smarter
than your roommate, who is the smartest? We are
Just need to determine the relationship
How do we solve linear syllogisms?
Spatial relationship between items
Semantic relationship between items
Categorical syllogisms
Probably most known
Premises state something about category membership of items
e.g. All cognitive psychologists are athletes, all athletes are pianists = all
cognitive psychologists are pianists
Doesn't have to be true, just logically valid
Often represented by Venn Diagrams
4 major types of premises:
Universal affirmative: all A are B
e.g. all humans are mammals
However, all B are A, is not necessarily true - depends on
All A are B, and all B are A scenario is not likely
Universal negative: no A are B
e.g. no humans are reptiles
Never intersect
Particular affirmative: some A are B
Some and possibly all
e.g. some humans are women
Could be a universal affirmative
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