Step 6 (and later, Step 7)

Example of depth test

• Schwarzenegger was born in Austria, so he can’t become the US President.

• Shallow reconstruction:– If Schwarzenegger was born in Austria, then he can’t become

US president.– Schwarzenegger was born in Austria.– So, Schwarzenegger can’t become US president.

• Deeper reconstruction:– Anyone born outside of the US can’t become US President.– Schwarzenegger was born in Austria.– So, Schwarzenegger can’t become US president.

Example of plausibility test

• Deeper reconstruction:– Anyone born outside of the US can’t become US President.– Schwarzenegger was born in Austria.– So, Schwarzenegger can’t become US president.

• Plausible reconstruction:– Anyone born outside of the US and whose parents aren’t

US citizens at the time of his/her birth can’t become US President

– Schwarzenegger was born in Austria.– So, Schwarzenegger can’t become US president.

Step 7

Example of Step 7

• Plausible reconstruction:– Anyone born outside of the US and whose parents aren’t US citizens

at the time of his/her birth can’t become US President– Schwarzenegger was born in Austria.– So, Schwarzenegger can’t become US president.

• Make this argument valid:– Anyone born outside of the US and whose parents aren’t US citizens

at the time of his/her birth can’t become US President– Schwarzenegger was born in Austria.– Austria is outside the US.– Schwarzenegger’s parents weren’t US citizens at the time of his birth.– So, Schwarzenegger can’t become US president.

INVALID!

VI.2. Nixon couldn’t have been president in 1950 because he was still in the Senate.1. Nobody can be president and a senator at

the same time.2. Nixon was a senator in 1950.3. Nixon could not have been president in

1950.

VI.18. His natural talents were not enough; he still lost the match because he had not practiced sufficiently.1. If he won the match, then he has natural

talents and practiced sufficiently.2. He did not practice sufficiently.*3. He did not win the match. *You could put a sub-argument here if you want a strict modus tollens, but I’m willing to give you a shortcut.

VI.18. His natural talents were not enough; he still lost the match because he had not practiced sufficiently.1. If a person’s natural talents are enough and

he/she does not practice sufficiently, then he/she will still win matches.

2. He did not win the match.3. So either he does not have enough natural

talent or he practiced sufficiently.4. He did not practice sufficiently. 5. His natural talents were not enough.

Digging deeper

• Assessing the truth of the premises• The regress problem• Fundamental principles• Exercises

Assessing the truth of the premises

• If you agree with premises, others may disagree. – So anticipating, reconstructing, & rebutting their objections is

a good way to solidify your argument.• If you disagree with the premises, then you need to

ascertain whether your rejection of the premises is more reasonable than your interlocutor’s. – So you need to reconstruct the best argument for that

premise.• So regardless of whether you agree/disagree with a

premise, you reconstruct the best argument you can for it.

The Regress Problem

• Not all premises can be assessed in this way.

• In philosophy, skeptics exploit this to pose a really nasty puzzle.

• Let’s take a look at this…

The Regress Problem, 1st Step

1. Suppose that you must justify p.2. You have three options:

a. Provide no justification for pb. Provide circular justification for pc. Justify p using some other proposition q.

3. If you provide (a) no justification for p, or (b) circular justification for p, then p is unjustified.

4. So if you must justify p, you must do so using some other proposition q.

The Regress Problem, 2nd Step

1. However, q can only justify p if q is itself justified.2. So you must justify q.3. You have three options:

a. Provide no justification for qb. Provide circular justification for qc. Justify q using some other proposition r…

4. So, for any proposition p that you must justify, you must provide an infinite chain of reasons.

5. You cannot provide an infinite chain of reasons.-----------------------------------------------------------------------6. So you cannot justify any proposition.

Solution to the Regress Problem

• Suppose that there are fundamental principles—principles that require no further justification.

• Example: – Fundamental Principle: Murder is wrong.– Abortion is murder. – Abortion is wrong.

IX.10. Morris does not deserve his wealth, for he merely inherited it.1. Anything inherited is not earned.2. Anything not earned is not deserved.3. Anything inherited is not deserved.4. Morris inherited his wealth.5. Morris does not deserve his wealth.

IX.12. There can’t be UFOs, because there is no life on other planets.1. If there are UFO’s, then they are vehicles

from other planets.2. Vehicles must be operated by organisms.3. No organisms from Earth operate UFO’s.4. If there are UFO’s, then organisms from other

planets must operate them.5. There are no organisms from other planets.6. There are no UFO’s.

XI.14. Parents take care of their children when they are young, so their children should take care of them when they get old.1. If x does a good deed for y, then y should perform an

identical good deed for x.2. Taking care of someone when they need it is a good

deed.3. If x takes care of y when y needs it, then y should take

care of x when x needs it.4. Parents take care of their children when they’re young

and need to be taken care of.5. Parents need to be taken care of when they’re old.6. Children should take care of parents when the latter

get old.

EXTRA EXERCISES.VI.1. Britney Spears is under age 35. Therefore she cannot run for president of the US.1. Anyone under the age of 35 cannot run for president of the US.2. Britney Spears is under the age of 35.3. Britney Spears cannot run for president of the US.

VI.6. There must not be any survivors, since they would have been found by now.1. If there were any survivors, they would have

been found by now.2. No survivors have been found by now.3. There are no survivors.

VI.8. Philadelphia cannot play LA in the World Series, since they’re both in the National League. 1. Teams from the same league cannot play

each other in the World Series.2. Philadelphia and LA are both in the National

League.3. Philadelphia and LA cannot play each other

in the World Series.

VI.17. This burglar alarm won’t work unless we are lucky or the burglar uses the front door, so we can’t count on it. 1. Burglar alarms that work only by luck or if a

burglar enters through the front door have limited coverage.

2. This burglar alarm works only by luck or if a burglar enters through the front door.

3. This burglar alarm has limited coverage.4. If a burglar alarm has limited coverage, then we

cannot count on it.5. We cannot count on the burglar alarm.