Psychology 3130A/B Lecture Notes - Lecture 7: Belief Bias, Confirmation Bias, Modus Tollens
22 Jun 2018
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Chapter 9 – Deduction
Deduction and Induction
-Deductive logic – attempting to explain how people make very specific conclusions
oStarts with a general statement/premise and then proceed to more specific statements/conclusions
oInvolves verifying which is already known
oCombined with additional premises and a conclusion, we can create an entire categorical syllogism
-Deductive statements assumed that the premise is true
oA valid deduction is one where the conclusion is the only possible conclusion given
the premise
oThere can be no other possible conclusion from these premises
Reasoning and Logic
-Reasoning is going beyond the given info to comprehend a situation
oMaking inferences and deductions
oTaking knowledge about what is known and drawing conclusions
oDiscovering something new by thinking
The Structure of a Logical Task
-A deductive statement (a syllogism) has several components
oOne or more premises – gives basic factual information that we can reason from and reason about
We assume they are true in a deductive task
Premise can contain facts and operators
Facts – things that can be true or things that can be false, descriptions, statements,
predicates
Operators – part of what make this different from inductive reasoning.
oEx. “or, and, not, if, all, some, none” – defines the nature of the deduction and
can modify the complexity of the argument
oConclusion
Start with “therefore” or “Then”
A valid conclusion is one in which the given conclusion is the only possibly conclusion given the
truth of premises
Invalid conclusion is one in where the same set of premises can give rise to more than one
possibly opposing conclusion
-Deduction can seem counterintuitive
oWe may agree with a stated conclusion even if it is not logically valid
oWe also may reject conclusions that are valid
oWe may agree with a valid conclusion for idiosyncratic reasons
oFailure to accept the logical task – often people don’t accept a logical argument because of their own
beliefs and understanding of the world
oA way to evaluate a conclusion is to replace facts with variables
oEX:
Premise 1: it is important to talk about things that are on our mind
Premise 2: household problems are on our mind
Conclusion: it is important to talk about household problems
oChange to:
Premise 1: it is important to do A
Premise 2: B is equal to A
Conclusion: it is important to do B
oPeople place a heavy premium in the content of the task
oNaïve reasoners with no training in formal thought may make many cognitive errors in reasoning and yet
still manage to achieve their goals and make good decisions
The fundamental paradox of rationality
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Deductive statements assumed that the premise is true: a valid deduction is one where the conclusion is the only possible conclusion given the premise, there can be no other possible conclusion from these premises. Reasoning is going beyond the given info to comprehend a situation: making inferences and deductions, taking knowledge about what is known and drawing conclusions, discovering something new by thinking. A deductive statement (a syllogism) has several components: one or more premises gives basic factual information that we can reason from and reason about. We assume they are true in a deductive task. Facts things that can be true or things that can be false, descriptions, statements, predicates. Operators part of what make this different from inductive reasoning: ex. Or, and, not, if, all, some, none defines the nature of the deduction and can modify the complexity of the argument: conclusion.
