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PHLA10 Chapter : PHLA10 Reason and Truth Exercise 2

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William Seager

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PHLA10 Reason and Truth
Exercise 2
1. Here's a little logical puzzle: you are in a strange land where everyone is either a knight or a knave.
Knights always tell the truth; knaves always lie. You meet two of them, A and B. A says "we are both
knaves". What are A and B? Prove it.
A is a knave and B is a knight. It is because A says the they are both knaves a knight cannot lie meaning A
is not a knight, but a knave can only lie and the statment was "we are BOTH knaves" they are not both
knaves, only one of them is and that is A. Since A told a lie B must be a knight.
2. What are the four main characteristics of God as Aquinas understood it?
3. What is the primary difference between the conception of motion that Aquinas accepted and Newton's
conception of motion?
Aquinas said that any movement requires a cause and that the first cause cannot be another moving body,
so it is something beyond our world this is God. Newton said that it is not motion itself that requires action,
but rather, it is changes in motion.
4. Explain why the "Birthday Fallacy" is a fallacy.
The birthday fallacy assumes that because every person has a single day on which he or she is born, that
there is a single day that is everybody's birthday.
5. What is the valid deductive logical form of a reductio ad absurdum argument?
Reductio ad absurdum is a type of logical argument where we assume a claim for the sake of argument,
arrive at an absurd result, and then conclude the original assumption must have been wrong, since it gave
us this absurd result.
6. What is the difference between necessity and contingency?
The contingent is what might not have existed. The necessary is what must exist.
7. What is a "necessary being"? Explain in terms of possible worlds
A necessary being exists in all possible worlds. For example, 1+1=2. This exists in all worlds, there are no
worlds where 1+1 does not equal 2
8. Why does Sober say that certainty is in the subjective realm while necessity is objective?
Certainty is in the subjective realm because it is expressed by doubting and saying that a proposition might
not be true. Necessity and contingency are objective. The degree of certainty may change, but there is only
the possibility of something to exist or not exist, and this cannot be changed. Necessity is similar to truth, in
that they are both objective issues independent of what people believe.
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