A unless B
~B――A
A unless B is a rather complex structure. Though surprisingly we use it with little thought or confusion in our day-to-day speech.
To see that A unless B is equivalent to ~B――A, consider the following situation:
Biff is at the beach unless it is raining.
Given this statement, we know that if it is not raining, then Biff is at the beach. Now if we symbolize Biff is at the beach as B, and it is rainingas R, then the statement can be diagrammed as ~R――B.
CLASSIFICATION
In Logic II, we studied deductive arguments. However, the bulk of arguments on the GMAT are inductive. In this section we will classify and study the major types of inductive arguments.
An argument is deductive if its conclusion necessarily follows from its premises――otherwise it is inductive. In an inductive argument, the author presents the premises as evidence or reasons for the conclusion. The validity of the conclusion depends on how compelling the premises are. Unlike deductive arguments, the conclusion of an inductive argument is never certain. The truth of the conclusion can range from highly likely to highly unlikely. In reasonable arguments, the conclusion is likely. In fallacious arguments, it is improbable. We will study both reasonable and fallacious arguments.
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