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Logical Deduction — Questions and Answers

Logical Deduction is syllogism in its formal dress: two premises about categories, and a set of conclusions to test. A conclusion follows only if it holds in every arrangement the premises permit. Venn diagrams settle these definitively, and two structural rules — no conclusion from two particulars, none from two negatives — dispose of many questions instantly.

10 solved questionsLogical ReasoningFree · no signup

Logical Deduction— Concepts, Formulas & Shortcuts

  • Draw Venn diagrams; a conclusion must hold in EVERY valid diagram.
  • Two particular premises ("some…some…") yield no definite conclusion.
  • Two negative premises yield no definite conclusion.
  • "All A are B" validly converts to "Some B are A".
  • "No A is B" validly converts to "No B is A".
  • If the premises are both universal, the conclusion cannot be particular unless existence is assumed.

Logical Deduction Practice Questions with Answers

Attempt each question first, then open the explanation. All 10 questions below are free to read and require no signup.

  1. Q1.Premises: All dogs are animals. All animals need food. Conclusion: All dogs need food.

    Easy
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DPartially follows
    +Show Answer & Explanation

    Answer: A. Follows

    Explanation: The chain dogs → animals → need food makes the conclusion valid.

    Logical Deduction question 1 of 10

  2. Q2.Premises: Some pens are red. All red things are bright. Conclusion: Some pens are bright.

    Moderate
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DNever follows
    +Show Answer & Explanation

    Answer: A. Follows

    Explanation: The pens that are red must be bright, so at least some pens are bright.

    Logical Deduction question 2 of 10

  3. Q3.Premises: All squares are rectangles. Conclusion: All rectangles are squares.

    Easy
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DSometimes follows
    +Show Answer & Explanation

    Answer: B. Does not follow

    Explanation: Converting a universal statement is invalid; rectangles form the larger class.

    Logical Deduction question 3 of 10

  4. Q4.Premises: No bird is a fish. All fish swim. Conclusion: No bird swims.

    Difficult
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DPartially follows
    +Show Answer & Explanation

    Answer: B. Does not follow

    Explanation: Birds are excluded from fish, but other swimmers may exist — ducks swim without being fish.

    Logical Deduction question 4 of 10

  5. Q5.Premises: Some books are novels. Some novels are long. Conclusion: Some books are long.

    Moderate
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DAlways follows
    +Show Answer & Explanation

    Answer: B. Does not follow

    Explanation: Two particular premises give no definite conclusion; the overlapping groups need not coincide.

    Logical Deduction question 5 of 10

  6. Q6.Premises: All metals conduct electricity. Copper is a metal. Conclusion: Copper conducts electricity.

    Easy
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DPartially follows
    +Show Answer & Explanation

    Answer: A. Follows

    Explanation: A universal premise applied to a specific member yields a valid conclusion.

    Logical Deduction question 6 of 10

  7. Q7.Premises: All roses are flowers. Conclusion: Some flowers are roses.

    Moderate
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DInvalid conversion
    +Show Answer & Explanation

    Answer: A. Follows

    Explanation: "All A are B" validly converts to "Some B are A".

    Logical Deduction question 7 of 10

  8. Q8.Premises: No student is lazy. All lazy people sleep late. Conclusion: No student sleeps late.

    Difficult
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DAlways follows
    +Show Answer & Explanation

    Answer: B. Does not follow

    Explanation: Students are excluded from the lazy group, but non-lazy people may also sleep late.

    Logical Deduction question 8 of 10

  9. Q9.Premises: All teachers are graduates. Some graduates are researchers. Conclusion: Some teachers are researchers.

    Moderate
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DAlways follows
    +Show Answer & Explanation

    Answer: B. Does not follow

    Explanation: The researcher graduates may lie entirely outside the teacher group.

    Logical Deduction question 9 of 10

  10. Q10.Premises: No reptile is warm-blooded. All snakes are reptiles. Conclusion: No snake is warm-blooded.

    Moderate
    • AFollows
    • BDoes not follow
    • CCannot be determined
    • DPartially follows
    +Show Answer & Explanation

    Answer: A. Follows

    Explanation: Snakes fall inside reptiles, which are wholly excluded from warm-blooded creatures.

    Logical Deduction question 10 of 10

Logical Deduction — Frequently Asked Questions

Why do two particular premises give no conclusion?+

Because "some A are B" and "some B are C" leave open whether the overlapping regions are the same. The As that are Bs need not be the Bs that are Cs.

What conversions are always valid?+

"All A are B" gives "Some B are A", and "No A is B" gives "No B is A". Converting "All A are B" into "All B are A" is the classic invalid step.

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