PHIL
1500 - Critical Thinking
Unit 1: Diagraming Arguments
Dr. Donald Nute
Strategies for Diagraming Arguments
1. Start by numbering all the statements in the argument.
2. Identifying the main conclusion. What is the writer trying to get you to believe? Conclusion indicators like so, thus, and therefore are helpful.
3. Identify premises or reasons that are put forward to support the main conclusion. Premise indicators like since and because are helpful.
4. Remember that the same sentence can serve as both a conclusion for one step of an argument and a premise for another step.
| (1) Dodd killed the mayor. (2) He had a motive. (3) The mayor worked against him in his campaign to get reelected to city council. (4) He had the means. (5) He owned a gun of the same caliber that killed the mayor. And (6) he had opportunity. (7) Witnesses saw him enter the mayor's office the night of the murder. |
5. Two premises provide independent support for a conclusion if either would still provide support if the other were discovered to be false.
| (1) Jones stole money from his boss and (2) deserted his family. (3) Jones is a bad man. |
6. Two premises provide joint support for a conclusion if one premise would not support the conclusion if the other premise were removerd.
| (1) Smith took out a loan. (2) He bought a new car and (3) he didn't have enough cash to pay for a new car. |
7. Here is one way to figure out whether two premises support a conclusion independently or jointly. Joint support usually involves some subject or topic that occurs in both premises but not in the conclusion. Without some subject or concept that links the two (or more) premises together, we usually are looking at a case where premises support the conclusion independently.
|
(1) Murphy did not study for his history exam. (2) People who do not study for an exam tend to receive a low mark. So (3) Murphy probably received a low mark on his history exam.
|
| (1) Perez plans to go home this weekend. And (2) she doesn't like football. So (3) Perez probably won't attend the football game this Saturday. |
| (1) Chang is taking metaphysics. (2) Most people who take metaphysics are philosophy majors. (3) Philosophy majors receive a bachelor of arts degree when they graduate. So (4) Chang will probably receive a bachelor of arts when he graduates. |