Logical Deduction Flashcards

Either the witness is lying or the evidence was planted. The witness is telling the truth. What follows?

Answer: The evidence was planted

In a disjunction, if one option is false, the other must be true; so if the witness is not lying, the evidence was planted.

All felonies carry imprisonment. This offence does not carry imprisonment. Therefore:

Answer: This offence is not a felony

By contrapositive: if not imprisoned, then not a felony — the offence is not a felony.

Most lawyers earn more than teachers. James is a lawyer. Which is the most logically warranted conclusion?

Answer: James probably earns more than most teachers

Since most (not all) lawyers earn more, James is probably in that majority but it is not certain.

Passage: 'Speed cameras reduce accidents only where drivers know they are installed.' Which scenario most weakens this claim?

Answer: An unmarked camera site sees a 35% accident drop

An unmarked camera reducing accidents contradicts the claim that awareness is necessary for the effect.

If the statute is ambiguous, the court applies the literal rule. The statute is clear. What can be concluded?

Answer: Nothing can be concluded about which rule applies

The conditional tells us what happens when the statute IS ambiguous; it says nothing about what happens when it is clear.

Five suspects — A, B, C, D, E — are ranked by likelihood of guilt. C is more likely than D. B is less likely than E. A is more likely than B but less likely than C. Which is the correct order from most to least likely?

Answer: C, A, E, B, D

C > D; E > B; C > A > B gives C > A > B with E > B, and C > D; combining: C, A, E, B, D is consistent.

Argument: 'Jury trials are expensive; therefore they should be abolished.' Which flaw does this argument commit?

Answer: Non sequitur — cost alone does not justify abolition

The conclusion (abolition) does not follow from cost alone without additional premises linking cost to abolition.