LSAT Logic and the Velocity of an Unladen Swallow

LSAT Blog Velocity LSAT Logic Unladen SwallowIn the movie Monty Python and the Holy Grail, there's a scene during Arthur's quest in which he encounters a bridge-keeper.

The bridge-keeper asks him, among other things, "what is the airspeed velocity of an unladen swallow?"

Bridge-keeper: Stop! What is your name?
King Arthur: It is Arthur, King of the Britons.
Bridge-keeper: What is your quest?
King Arthur: To seek the Holy Grail.
Bridge-keeper: What is the air-speed velocity of an unladen swallow?
King Arthur: What do you mean? An African or European swallow?
Bridge-keeper: What? I don't know that! [falls into abyss]
Sir Bedemir: How do know so much about swallows?
King Arthur: Well, you have to know these things when you're a king, you know.
Now, this is funny, but why am I talking about it?

Arthur's response is an interesting argumentative technique, and Bedemir commits a logical fallacy. Both of their responses are related to types of reasoning we see on the LSAT.


Rather than attempt to answer the question or admit that he doesn't know the answer, Arthur simply responds with a question of his own. The bridge-keeper happens to be shocked by the question and doesn't know how to deal with it.

Arthur's response doesn't actually demonstrate any knowledge related to the velocity of unladen swallows at all, other than to suggest that perhaps he knows that the velocities of African and European swallows differ.

Bedemir is far more impressed with Arthur's response than he should be. He improperly assumes that it indicates Arthur knows something significant about the unladen swallows' airspeed velocity.

Arthur's response serves as irrelevant evidence when it comes to supporting the conclusion that he knows a great deal about swallows.

In order to properly conclude that Arthur knows something about the velocity of unladen swallows, we'd have to actually hear him say something related to their actual speed. Even if we didn't hear a firm number (such as "20 kilometers per hour") the response that it's "the same as that of a 10-year-old child riding a bicycle" would serve as much firmer evidence than what Arthur asked. (These guys did a good job of suggesting they know what they're talking about.)

See PrepTest 36 (December 2001 LSAT), Section 1, Question 12, page 257 in Next 10) for an example of an actual LSAT question where the evidence provided gives us little reason to support the conclusion.

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