Socratic Logic - Reasoning

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.

Enthymemes - Abbreviated Syllogisms

An enthymeme is a syllogism where one of the three propositions is left out.  This is done for either simplicity sake or because the proposition is assumed.

A first order enthymeme leaves out the major premise.

A second order enthymeme leaves out the minor premise.

A third order enthymeme leaves out the conclusion.

Finding the Missing Premise

You cannot test for the validity of an argument if there is a missing premise.

A very important skill in logic is determining if an argument has hidden assumptions.

Follow these steps to try and find missing premises:

A. Be sure there really is a missing proposition.

B. Identify the conclusion first, rarely is it left out. (ie. advertising)

C. Put it into logical form.

D. Identity the missing premise or conclusion.

E. If there is an argument, deduce the common (minor) term.

1. All pronouns should be converted to nouns.

2. Synonyms should be changed to one word.

3. Change word order if necessary.

4. Reword possessives as independent nouns.

F. Once two non-hidden propositions are written out and common term found, find the missing premise.