Socratic Logic - Induction

Arguments from Analogy

The following are the notes I have taken from Peter Kreeft's wonderful Socratic Logic textbook. I highly recommend you buy it. This is a book which deals with classical logic (as opposed to modern symbolic logic.) It is easily the best overall book on logic I have ever read and one of the few I have that are worth making notes from. I even have a small duotang with these notes in it I can carry around and reference on a regular basis.

Many analogies are meant as arguments but as explanations or illustrations.  They have more power as explanations than as arguments.   Analogies are the most widely used form of inductive argument.  They are usually a mixture of induction and deduction.

What is an Argument from Analogy?

A. The premises of an argument from analogy are observed similarities between two or more things in one or more ways.

B. The conclusion is that they would be alike in another way.

Criteria That Make Arguments from Analogy More Probable

A. Number of entities observed in premises.

B. Variety of entities observed in premises.

C. Number of attributes in which entities are similar.

D. Relevance of known attributes.

E. Number, variety and importance of dissimilarities between entities. (Negative factor)

F. Boldness of conclusion claimed.

Refutation by Logical Analogy

You can show an argument is invalid by showing another argument of exactly the same form is also invalid.  Similar to the reductio ad absurdum.