Syllogisms and Logic

PART I: SYLLOGISMS

To be a valid syllogism, the conclusion must be proven by the reasons. Carefully study the following syllogisms and decide if they are valid or invalid:

1. All zebras are striped animals.
No zebras are polar bears.

Therefore, no polar bears are striped animals.

2. All clowns are funny individuals.
Some sad people are clowns.

Therefore, some sad people are funny individuals.

3. Some sticky substances are yucky things.
All taffy is a sticky substance.

Therefore, some taffy is a yucky thing.

4. All items made of gold are expensive items.
Some rings are items made of gold.

Therefore, some rings are expensive items.

5. All flies are winged creatures.
All butterflies are winged creatures.

Therefore, all butterflies are flies.

The following are examples of syllogistic arguments that are missing the conclusions. Study the two reasons very carefully and complete the syllogism with the conclusion that logically follows.

1. All fragile things are breakable things.
Some glasses are fragile things.

Therefore

2. All mammals are warm-blooded animals.
All whales are mammals.

Therefore

3. All books are things with pages.
Some books are mysteries.

Therefore

4. All flowers are pretty objects.
All pansies are flowers.

Therefore

5. No animals are plants.
All sheep are animals.

Therefore

Reprinted with permission of the authors Elizabeth T. Tice, PhD and Jay Gallagher, PhD.

PART II: LOGIC & EMOTION QUESTIONS:

There are two ways to make an argument: through inductive and deductive reasoning. Answer the questions below.

Deductive Argument

1. What makes an argument deductive?
2. Why do people use deduction?

3. Create a deductive argument. Label its parts

Inductive Arguments

1. What makes an argument inductive?
2. Why do people use induction?

3. Create an inductive argument. Label its parts.

Emotion

1. What role does emotion play in the critical thinking process?

2. What is the difference between persuasion and manipulation?

Part III: FALLACIES

Fallacies, or fallacious reasoning, are an attempt to convince others of our point of view. Using the List of Common Fallacies, identify the fallacies used in the examples below.

1. Of course she's rich! Just look at that diamond ring she is wearing.

2. The United States is a wealthy country; therefore, Sam Jones must be wealthy.

3. Every attempt to prove that people are immortal has failed. No evidence can be found that shows that people's souls exist after death; hence, immortality must be false.

4. If Jennifer Aniston drinks a Starbucks latte, it must be good.

5. If you are going to work on the weekends to finish one project, then you may as well start working every weekend.

6. I love visiting Wyoming because I enjoy traveling in the West.