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SYLLOGISMS: Deductive Reasoning

Remember: There is a difference between asserting that a premise is untrue and asserting that the logic of the argument is faulty. “All dogs can fly. Fido is a dog. Fido can fly.” That is a perfectly valid argument in terms of logic, but this flawless logic is based on an untrue premise. If a person accepts the major and minor premises of an argument, the conclusion follows undeniably by the sheer force of reason. If in an argument, the logic reaches a conclusion that seems absurd, it behooves you to analyze each sentence separately (to see if each premise is true without exception) and then to analyze the structure of the argument (to see if the reasoning of the argument itself is valid). Also be on the lookout for “equivocation,” the use of two different meanings of one word during the process of an argument. APA Format

Directions: Pick 5 of the following syllogisms. For each syllogism:

1. Identify the following:

a. Major premise

b. Minor premise

c. Conclusions

d. Major term

e. Minor term

f. Middle term

2. Decide whether the syllogisms are valid in format (as opposed to using true premises).

3. Explain why the syllogism is valid or invalid. You can use a Venn diagram, transference of

middle terms, or illustrate using circles.

Invalid example: All snakes are cold-blooded. Valid example: All humans are selfish. All snails are cold-blooded. Confucius is a human. All snails are snakes. Confucius is selfish.

INVALID: Snakes and snails could VALID. We might not agree that the individual overlap as categories, but they both could also premises are true, but if we accept these be in the largest circle without overlapping. premises, the conclusion does logically follow.

1. All human societies are doomed to deteriorate over time. America is a human society.

Snails

Snakes

Cold-blooded things

Confucius

Humans

Selfish Things

America is doomed to deteriorate over time.

2. No philosophers are evil. All Greeks are philosophers. No Greeks are evil

3. All women are potential mothers. Betty is a potential mother. Betty is a woman.

4. All students are eligible for student government. No teachers are eligible for student government. No teachers are students.

5. All barbiturates are drugs. Marijuana is not a barbiturate. Marijuana is not a drug.

6. Pizza is a substance made of cardboard. All substances made of cardboard are good to eat. Pizza is a substance that is good to eat.

7. All rational people believe in rule by law. Some rational people are college professors. Some college people are believers in rule by law.

8. All purple items are green. All yellow items are green. All purple items are yellow.

9. Violent television influences some children in negative ways. Some children are violent. Some children are influenced by violent television.

10. Laughter is a meretricious act. All meretricious acts are melancholic in nature. Laughter is melancholic in nature.

11. All environmentalists are activists. Some activists are uninformed. Some environmentalists are uninformed.

12. As Emerson said, "All the world loves a lover." Now that I think about it, Susan is a part of the world. I am a lover, now that I think about it. Susan must love me! The logic is irresistible!

13. Nothing is better than God. Having a lobster is better than having nothing. Lobsters are better than God.

14. God is love.

Love is blind. Ray Charles is blind.

Ray Charles is God.