Either Or Conclusions in Reasoning: Complementary Pair Rule, Tricks and Solved Questions for SSC

In statement-conclusion and syllogism questions, one of the options is "Either I or II follows". This option is chosen only under special conditions, and most students lose marks because they use it wrongly or never use it. These either-or conclusions reasoning tricks for SSC give the three conditions, the pairs that make a complementary pair, and solved examples.

The Three Conditions of the Either-Or Case

1. The two conclusions have the same subject and the same predicate (they talk about the same two things).
2. The two conclusions form a complementary pair (one is the negation of the other).
3. Neither conclusion follows alone from the statement.

If all three conditions are true, the answer is "Either I or II follows".

Complementary Pairs

Solved Examples

Example 1. Statement: Some pens are books.
I: All pens are books. II: Some pens are not books.
The subject and predicate are the same (pens, books). The pair "All A are B" and "Some A are not B" is a complementary pair. Neither follows from the statement alone. Either I or II follows.

Example 2. Statement: The people of the city are rich.
I: The people of the city are rich. II: The people of the city are not rich.
I follows directly from the statement, so the answer is Only I follows. The either-or option is not used, because one conclusion already follows.

Example 3. Statement: A new chemical has been tested on 100 animals.
I: The chemical is harmful for humans. II: The chemical is not harmful for humans.
The pair is complementary, and neither follows from the statement. Either I or II follows.

Example 4 (inequality). Statement: M ≥ N.
I: M > N. II: M = N.
The statement says M > N or M = N, and one of them must be true. Either I or II follows.

Example 5. Statement: All birds are animals.
I: Some birds are not animals. II: Some animals are birds.
I is false. II follows. The pair is not complementary here, so the answer is Only II follows.

Common Mistakes

• Using "either or" when one conclusion already follows.
• Using "either or" for two conclusions with different subjects.
• Using "either or" when both conclusions are false for a reason that is stated in the statement.

Quick Tips

• Check the three conditions every time.
• First test whether one conclusion follows alone.
• The two conclusions must be about the same subject and predicate.
• Learn the complementary pairs in the table.

Quick Revision Points

• The either-or case needs the same subject and predicate.
• The two conclusions must be a complementary pair.
• Neither conclusion should follow alone.
• All A are B and Some A are not B is a complementary pair.
• In inequality, M > N and M = N together give M ≥ N.

Practice Questions With Answers

1. Statement: Some pens are books. I: All pens are books. II: Some pens are not books. Which option is correct?
   Answer: Either I or II follows
2. Statement: A new drug has been tested. I: The drug is harmful. II: The drug is not harmful. Which option is correct?
   Answer: Either I or II follows
3. Statement: All birds are animals. I: Some birds are not animals. II: Some animals are birds. Which option is correct?
   Answer: Only II follows
4. Statement: M ≥ N. I: M > N. II: M = N. Which option is correct?
   Answer: Either I or II follows
5. Is All A are B and Some A are not B a complementary pair?
   Answer: Yes
6. Is No A is B and Some A are B a complementary pair?
   Answer: Yes
7. How many conditions are there for the either-or case?
   Answer: Three
8. Can the either-or option be chosen when one conclusion follows?
   Answer: No
9. Can the either-or option be chosen for two conclusions with different subjects?
   Answer: No
10. What is the first check in an either-or question?
    Answer: Check if any conclusion follows alone

How to Practise This Chapter

Practise 10 questions every day and write the steps on paper. Then attempt timed sets from our practice papers and the previous year papers page. See all topics on the Logical Reasoning notes page, read the previous topic Statement and Inference and the next topic Inequality Reasoning. Also read the Reasoning notes. Also read Syllogism and Statement and Conclusion.

Frequently Asked Questions

What is the either-or case in reasoning?

It is the case in which one of the two complementary conclusions must be true, though neither follows alone.

What are the conditions of the either-or case?

Same subject and predicate, a complementary pair, and neither follows alone.

What is a complementary pair?

It is a pair of conclusions in which one is the negation of the other, like "All A are B" and "Some A are not B".

When is the either-or option wrong?

When one of the conclusions follows alone, or when the conclusions are about different things.

Does the either-or case work in inequality?

Yes. For example, M > N and M = N are an either-or pair for M ≥ N.

Is the either-or case used in syllogism?

Yes. It is used in syllogism questions with the pairs Some and No.

What if both conclusions follow?

Then the answer is "Both follow".

What if neither follows and they are not a complementary pair?

Then the answer is "Neither follows".

Is this topic asked in SSC exams?

Yes. It is part of statement-conclusion and syllogism questions.

How much time should I take?

About 30 seconds.

What are the common mistakes?

Not checking whether one conclusion follows alone.

How can I practise?

Solve 10 statement-conclusion questions daily and find the either-or case in each.