Q.9 Given below are two statements 1 and 2, and two conclusions I and II.
Statement 1: All bacteria are microorganisms.
Statement 2: All pathogens are microorganisms.
Conclusion I: Some pathogens are bacteria.
Conclusion II: All pathogens are not bacteria.
Based on the above statements and conclusions, which one of the following
options is logically CORRECT?
(A) Only conclusion I is correct
(B) Only conclusion II is correct
(C) Either conclusion I or II is correct.
(D) Neither conclusion I nor II is correct
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Understanding the Logic Question
This classic syllogism tests your ability to draw valid conclusions from two statements using set theory and Venn diagrams. The question appears in competitive exams like UPSC, SSC, banking reasoning tests, and academic assessments.
Statements:
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Statement 1: All bacteria are microorganisms.
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Statement 2: All pathogens are microorganisms.
Conclusions:
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I: Some pathogens are bacteria.
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II: All pathogens are not bacteria.
Options:
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(A) Only conclusion I is correct
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(B) Only conclusion II is correct
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(C) Either conclusion I or II is correct
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(D) Neither conclusion I nor II is correct
Visualizing with Venn Diagrams
Both bacteria and pathogens are entirely contained within microorganisms, but their relationship to each other remains undefined. Here’s the key insight:
Microorganisms (Large Circle)
├── Bacteria (100% inside microorganisms)
└── Pathogens (100% inside microorganisms)
Possible overlaps:
1. Bacteria and pathogens completely overlap
2. No overlap between bacteria and pathogens
3. Partial overlap
The statements guarantee both sets are subsets of microorganisms but say nothing about intersection between bacteria and pathogens.
Correct Answer: (B) Only Conclusion II is Correct
Conclusion I (“Some pathogens are bacteria”) is INVALID
This assumes overlap exists. However, pathogens could occupy a completely separate region within microorganisms. No overlap is guaranteed, so this doesn’t necessarily follow.
Conclusion II (“All pathogens are not bacteria”) is VALID
In logical reasoning, “All X are not Y” means “No X are Y” or “X and Y are disjoint sets.” Since the statements allow for zero overlap between pathogens and bacteria (both fitting entirely within microorganisms), this scenario is possible. Therefore, Conclusion II logically follows as a valid possibility.
Why Other Options Fail
Option (A) Only conclusion I is correct ❌
Wrong because I doesn’t follow—pathogens might not overlap with bacteria at all.
Option (C) Either conclusion I or II is correct ❌
Invalid because both cannot be true simultaneously. “Some overlap” (I) and “No overlap” (II) are mutually exclusive. Logic questions never use “either/or” for contradictory conclusions.
Option (D) Neither conclusion I nor II is correct ❌
Wrong because II is valid, as the no-overlap scenario fits the statements perfectly.
Common Mistakes to Avoid
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Assuming overlap exists: Shared superclass (microorganisms) doesn’t imply subclass intersection.
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Misinterpreting “All pathogens are not bacteria”: This is standard logic shorthand for “No pathogens are bacteria,” which remains possible.
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Ignoring extreme cases: Always test boundary scenarios (complete overlap, no overlap, partial).
Practice Tip for Exams
Draw quick Venn diagrams for “All A are C” + “All B are C” questions. The correct conclusion is typically the disjoint possibility unless overlap is explicitly stated.
Quick Test: Can you create bacteria that are pathogens? Yes. Can you create pathogens that aren’t bacteria? Yes. Neither is required, so only the “no overlap” conclusion holds.
