Logic & Critical Reasoning Quiz 1

What is a logical argument?

A claim defending another claim

2 Premise Indicator words

1. Since

2. Because

2 Conclusion Indicator words

1. So

2. Therefore

What are possible ways an argument can be invalid?

If the premises are false

True or False: A sound deduction may have one false premise

False; a sound deduction requires all true premises.

All dogs are reptiles; Fido is a dog; therefore, Fido is a reptile.

Argument

Go to your room, because you have been bad, and all bad persons must go to their rooms.

Explanation

Water freezes at 32 degrees because the molecules get so cold that they slow down enough to hook onto each other, forming a solid crystal.

Explanation

Can an unsound deduction have a true premise?

Yes

Can an unsound premise have all untrue premises?

Yes

Deduction Chart

-Necessary > Valid/ Invalid

-Valid > Sound/ Unsound

-Invalid > Unsound

Induction Chart

-Probability > Strong/ Weak

-Strong > Cogant/ Uncogant

-Weak > Uncogant

Deduction: Valid/ Sound Example

All cats are mammals

Felix is a cat

Therefore, Felix is a mammal

Deduction: Valid/ Unsound Example

All cats are reptiles

Felix is a cat

Therefore, Felix is a reptile

Deduction: Invalid/ Unsound Example

All cats are mammals

Felix is a reptile

Therefore, Felix is a cat

Induction: Strong/ Cogant Example

Most cats are playful

Felix is a cat

Therefore, Felix is likely playful.

Induction: Strong/ Uncogant Example

Many cats enjoy climbing trees

Felix is a cat

Felix will likely enjoy climbing trees

Induction: Weak/ Uncogant Example

Only a few cats seen at a local shelter were orange,

which leads to the conclusion that most cats must be orange

Compose an enthymeme, then supply the missing premise

All cats are mammals

Therefore, all cats are warm-blooded

Missing Premise: All mammals are warm-blooded

Write an argument that attempts to leap over the “is-ought gap.”What missing premise would make it valid?

People often seek happiness

Therefore, we should pursue activities that increase happiness

Missing Premise: Activities that increase happiness contribute positively to well-being