University:
Manchester University
Course:
PSYC 110 | Introduction to Psychology
Academic year:

2023
Views:

500

Pages:

12
Author:

Clint W.

Inductive Logic Inductive Logic Overview (1) Distinguish inductive from deductive arguments (2) Define ‘strength’ and ‘cogency’ (3) Describe four kinds of inductive arguments (4) Practice exercises on inductive logic Deductive and Inductive Arguments Deductive vs Inductive Deductive Reasoning • Formal (the inference can be assessed from the form alone). • When sound, the conclusion is guaranteed to be true. • The conclusion is extracted from the premises. Inductive Reasoning • Informal (the inference cannot be assessed by the form alone). • When cogent, the conclusion is only probably true. • The conclusion projects beyond the premises. Deductive vs Inductive: Certainty Inductive arguments have conclusions that are uncertain… (1) This swan is white. (2) That swan is white. ∴ (3) The next swan I see will be white. Deductive vs Inductive: Certainty Inductive arguments have conclusions that are uncertain… (1) This swan is white. (2) That swan is white. ∴ (3) The next swan I see will be white. … but so do many deductive arguments. (1) Alice owns a swan. (2) All swans are white. ∴ (3) Alice’s swan is white. With inductive arguments, the uncertainty lies in the inference. With deductive arguments, the uncertainty lies in one or more of the premises. Strength and Cogency Strength • A property of the argument. • If an argument is strong, then the truth of the premises guarantees the probable truth of the conclusion. • Unlike validity (which is all or nothing), inductive strength comes in degrees, and is determined by the content of the premises. Cogency • A property of the argument. • If an argument is cogent, then (1) it is strong, and (2) all of its premises are true. Strength and Cogency Deductive Logic Inductive Logic • Valid/Invalid inferences • Strong/Weak inferences • Sound/Unsound arguments • Cogent/Uncogent arguments • Conclusions are guaranteed true. • Conclusions are probably true. Sample Inductive Arguments Common CommonInductive Inductive Reasoning Reasoning Generalization Inferring your beliefs about the whole of X from a part of X. Authority Inferring your beliefs about X from the beliefs held by a trusted source. Analogy Inferring your beliefs about a lesser known thing from its similarities with a better known thing. Hypothetical Induction Discovering the best explanation for some thing or event. Agument from Generalization Argt. from Generalization (1) Token 1 of type A has property X. (2) Token 2 of type A has property X. Token = an individual Type = a class of individuals ∴ (3) All tokens of type A have property X. [or] ∴ (3’) The next token of type A will have property X. Agument from Generalization Argt. from Generalization (1) Token 1 of type A has property X. (2) Token 2 of type A has property X. Token = an individual Type = a class of individuals ∴ (3) All tokens of type A have property X. [or] ∴ (3’) The next token of type A will have property X. Example: (1) The first Twinkie I ate from this box of 24 Twinkies had its créme filling riddled with mouse droppings. (2) The second Twinkie I ate from the box was similarly contaminated. (3) Likewise with the third Twinkie. (4) Therefore, the next (fourth) Twinkie I eat from this box will likely also have mouse droppings in its crème filling.