Lecture 1

If something is gold, then it is metallic

• Being gold is necessary and sufficient for being metallic

• Being gold is necessary but not sufficient for being metallic

• Being gold is sufficient but not necessary for being metallic

• Being gold is neither necessary nor sufficient for being metallic.

Consider the following argument:

1. Anna scored 90 percent in the physics exam

2. Astrid scored 50 percent in the physics exam.

3. Hence, Anna is better at mathematics than Astrid

What kind of argument is this?

• Inductive argument

• Adbuctive argument

• Truth-preserving argument

• None of the above

Answer explanation

Anna’s being better at maths is a good explanation of the test scores. So theargument is abductive. But it’s possible for these test scores to occur, even if Anna isnot better at mathematics. (Maybe Anna was distracted.) So the conclusion of theargument could be false, even if the premises are true. So the argument isn’tdeductive.

Consider the following argument.

1. Anna scored 90 percent in the physics exam.

2. Anyone who scores above 80 percent in the physics exam is smart.

3. Hence, Anna is smart.

What kind of argument is this?

• Inductive argument

• Adbuctive argument

• Truth-preserving argument

• None of the above

Answer explanation

It’s impossible for the premises to be true, and the conclusion to be false. (Andthis is true for any argument of this form.) So the argument is truth-preserving.

Consider the following argument.

1. 90 percent of physicists like mathematics.

2. Anna is a physicist

3 Hence, Anna likes mathematics.

What kind of argument is this?

• An inductive argument

• An adbuctive argument

• A truth-preserving argument

• None of the above

Answer explanation

Plausible explanation based on statistics

Consider the following argument.

1. If it rains, then he will get wet.

2. He didn’t get wet.

3. Hence, it didn’t rain.

What kind of argument is this?

• Modus Ponens

• Modus Tollens

• Affirming the Consequent

• None of the above

What is the missing premise or premises in the following enthymeme?

1. All Mexicans speak Spanish

2. Hence, all Mexicans know what “tortuga” means.

Answer explanation

All people who speak Spanish know what “tortuga” means.

What is the missing premise or premises in the following enthymeme?

1. Rob lied to Ravi

2. Hence Rob is not a good friend to Ravi.

Answer explanation

Good friends do not lie to each other.