Question

Virginia and her brother William disagree over when their father was born: Virginia claims it was in 1935 and William claims it was in 1933. The hospital where their father was born has no records for 1933 but has complete records for 1935--records that do not include a birth record for their father. Therefore, he must have been born in 1933.
The argument depends on which of the following assumptions?

• A. Either Virginia's claim or William's claim is correct.
• B. The records of the hospital where their father was born date back to 1933.
• C. Virginia and William know the day and the month of their father's birth.
• D. There are urgent practical reasons why Virginia and William must know the date of their father's birth.
• E. None of their other relatives knows the year in which Virginia and William's father was born.

Hint:

Be on the lookout for arguments that present a "false dichotomy" -- that is, they pretend there are only two choices when in fact there could be more. The unstated assumption in such arguments is always that the two choices presented are the only ones.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This is a necessary assumption question. The argument concludes that the father must have been born in 1933. We need to find the unstated premise that is required for this conclusion to be valid.
Step 2: Key Formula or Approach:
The argument follows a process of elimination. It considers two possibilities (born in 1933 or 1935), eliminates one, and concludes the other must be true. This type of argument is only valid if the initial possibilities were the only possibilities.
Step 3: Detailed Explanation:
- Premise 1: Virginia says 1935; William says 1933.
- Premise 2: The hospital has complete 1935 records, and the father is not in them. This eliminates 1935 as a possibility (assuming he was born in that hospital).
- Premise 3: The hospital has no records for 1933 (so 1933 cannot be eliminated).
- Conclusion: Therefore, he must have been born in 1933.
The logical leap is from "It's not 1935" to "It must be 1933." This only works if 1933 and 1935 were the only two years under consideration. What if he was actually born in 1934, or 1936? The argument completely ignores these other possibilities. It implicitly assumes that one of the two siblings is correct.
- (A) This statement, "Either Virginia's claim or William's claim is correct," explicitly states this necessary assumption. If this is true, and Virginia's claim (1935) has been disproven, then William's claim (1933) must be the correct one.
- Negation Test: If we negate (A), "Neither Virginia's claim nor William's claim is correct," then the conclusion falls apart. If they are both wrong, then eliminating 1935 tells us nothing about whether 1933 is the correct year. He could have been born in any other year. Since negating the statement destroys the argument, (A) is a necessary assumption.
- (B), (C), (D), and (E) are all irrelevant to the logical structure of the argument, which hinges on the exclusivity of the two initial claims.
Step 4: Final Answer:
The argument works by eliminating one of two options. It therefore must assume that those two options were the only ones possible.