Difficulty: Medium
Correct Answer: None of the conclusions 1, 2, 3 or 4 necessarily follows.
Explanation:
Introduction / Context:
This syllogism question involves four categories: tapes, discs, cassettes and songs. You are given three statements of the form "some A are B" and several possible conclusions. Your task is to decide which conclusions must be true in every possible arrangement that satisfies the statements, not just in some imagined scenario.
Given Data / Assumptions:
Concept / Approach:
Each "some" statement only guarantees that an intersection is non empty; it does not tell us that the same object appears in multiple intersections. Therefore, the tape that is a disc, the disc that is a cassette, and the cassette that is a song can all be different objects. We must check whether any of the proposed conclusions are forced by the premises, or whether different valid diagrams can make them true or false.
Step-by-Step Solution:
Step 1: Imagine three distinct objects x, y and z defined as follows:
• x is both a tape and a disc (T ∩ D).
• y is both a disc and a cassette (D ∩ C).
• z is both a cassette and a song (C ∩ S).
These three satisfy all three given statements.
Step 2: In this construction:
• No song is a disc, because z is a cassette and a song, but not a disc, and x and y are not songs.
So S ∩ D = ∅ in this particular diagram.
Step 3: However, we could also construct another valid diagram where the cassette which is a song is also the disc that is a cassette, making at least one object in D ∩ S. In that alternative diagram, S ∩ D ≠ ∅. This shows that Conclusion 1 ("Some songs are discs") can be true in some models and false in others, so it is not logically necessary.
Step 4: Similar reasoning applies to Conclusion 2 ("Some cassettes are tapes") and Conclusion 3 ("Some songs are tapes"). The overlaps C ∩ T and S ∩ T may exist in some arrangements but need not exist in all. Our initial diagram with x, y and z chosen as distinct shows that these intersections can be empty while the given statements remain true.
Step 5: Consider Conclusion 4 ("No song is a disc"). In our first diagram, this is true, but we can easily adjust the diagram so that the cassette that is a song is also the disc that is a cassette, making at least one song a disc. Then Conclusion 4 becomes false while all three statements are still satisfied. Therefore, Conclusion 4 is also not necessary.
Verification / Alternative check:
The critical test in syllogism is not whether a conclusion can be true, but whether it must be true in every possible case that satisfies the premises. Because we can design one valid diagram where a conclusion holds and another valid diagram where it does not, the conclusion does not logically follow. Here, for each of the four conclusions, such alternative diagrams can be drawn, so none of them is guaranteed.
Why Other Options Are Wrong:
Options B, C and D each claim that one of the conclusions must follow, but this is disproved by the counterexamples described above. In some arrangements, those conclusions may happen to be true, but they are not forced by the given statements. Only Option A correctly states that none of the four conclusions is logically necessary.
Common Pitfalls:
A common mistake is to "chain" the premises informally: some tapes are discs, some discs are cassettes, some cassettes are songs, so students assume there is at least one object that is simultaneously a tape, disc, cassette and song. The premises never say that; they only guarantee pairwise overlaps which may involve different objects. Always remember that "some A are B" says nothing about all A or all B, and it does not guarantee multi way intersections unless specified.
Final Answer:
None of the conclusions 1, 2, 3 or 4 is logically forced by the premises, so none of the conclusions necessarily follows.
Discussion & Comments