PHL A10 - Exercise III
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 is A and B? Prove it.
A is a knave, and B is a knight. If A were a knight, then he would have to be telling the truth. He would be saying
that they were both knaves, but knaves always lie, hence this logic does not follow through. On the other hand, if
A were a knave, then he is lying about both of them being knaves. Since the statement is false, there is the
possibility that B is be a knight, while A is a knave. A would be lying about both of them being knaves, but it
does not mean that one of them cannot be a knave. The logic is successful in that the statement remains false
while abiding by the stated premises.
2. What are the four main characteristics of God as Aquinas understood it?
Aquinas described God as being a person who was omnipotent, omniscient, and omni-benevolent. These four
attributes were used to the understanding of God’s presence, knowledge, power, and integrity. This understanding
of God is used throughout various religions, such as Judaism, Christianity, and Islam to explain the existence of
this all-powering, all-knowing, and entirely good being.
3. What is the primary difference between the conception of motion that Aquinas accepted and Newton's
conception of motion?
Aquinas conception of motion was derived from Aristotle’s idea of physics. Aristotle stated that if an object
continues to move, a force that keeps it in motion must sustain its motion. Therefore, if the force was removed,
the obj ect stops moving. However, in modern physics, as explained by Newton’s conception of motion, he
describes that an object remains in constant uniform motion unless acted on by a force. The force acted on an
object with a certain mass will accelerate at a certain speed. Therefore, if there is no force acting on the object,
there is no acceleration, keeping the object stationary or in uniform motion. Aristotle and Aquinas believed
motion requires an outside force, whereas Newton’s theory states that it is acceleration that requires a force.
4. Explain why the "Birthday Fallacy" is a fallacy.
A fallacy is a com ponent of an argument that is demonstrably flawed in its logic or form, thus rendering the
argument invalid as a whole. The “Birthday Fallacy” is the mistaken idea where a second proposition does not
follow the first, where the first proposition could be true, while the second one is false. The idea that, “everyone
has a birthday”, does not deductively imply that there is a day that is everyone’s birthday, is the concept of the
“Birthday Fallacy”. Basically, it is a fallacy because the logic with this statement could make an argument invalid.
5. What is the valid deductive logical form of a reductio ad absurdum argument?
A reductio ad absurdum is the idea of reducing something to absurdity. In order to prove something true, one
argues as if P were false, then another idea would have to be true; however, this second idea has to be obviously
false, so that one can finally conclude the validity of the original idea. The valid deductive logical form of a
reductio ad absurdum argument is:
If P is false, then A is true.