Critical Thinking
Across the
Curriculum Project

Critical Thinking Core Concepts

Contributed by:  Michael Connelly, Longview Community College

Valid argument forms:

Modus Ponens- 

1. If A then B, 
2. A 
3. B (conclusion)

 Fallacious form: (affirming the consequent) 
1. If A then B, 
2. B
3. A
Modus Tolens- 
1. if A then B, 
2. Not B
3. Not A		 Fallacious form: (Denying the Antecedent) 
1. If A then B, 
2. Not A
3. Not B
Disjunctive Syllogism- 
1. A or B 
2. Not A
3. B		 Hypothetical Syllogism- 
1. if A then B 
2. if B then C
3. if A then C

Using Truth Tables to discover Validity:

If you look at the structure of any deductive argument, you will notice that each of them can be expressed as a conditional statement, with the conjunction of all the premises serving as the antecedent and the conclusion serving as the consequent. With this in mind, we can use truth tables to find out the validity of different argument forms which do not match (immediately) any of the known valid forms.

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Copyright © 1996
Critical Thinking Across the Curriculum Project
Longview Community College , Lee's Summit, Missouri - U.S.A.
One of the Metropolitan Community Colleges
An Equal Opportunity/Affirmative Action Employer

Permission to reproduce these resource pages is granted for
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Inquiries to: michael.connelly@mcckc.edu
Last modified: 03/02/04