Syllogism Practice — Valid & Invalid Conclusions

This is a practice bank for UCAT Decision Making syllogism questions. Work through the 10 questions below under timed conditions (~60 seconds each) before reviewing your answers.

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Quick-Reference: Syllogism Rules

A syllogism has two premises and a conclusion, linked by a middle term that appears in both premises but not in the conclusion.

The Four Statement Types

Code	Form	Example
A	All X are Y	All nurses are graduates
E	No X are Y	No students are consultants
I	Some X are Y	Some doctors are researchers
O	Some X are not Y	Some graduates are not employed

Validity Checklist

1. Draw a Venn diagram for each premise
2. Check whether the conclusion must follow — not just could follow
3. "Some" means "at least one" (not "a few" or "not all")
4. Ignore real-world knowledge — evaluate the logic only

Common Invalid Patterns to Watch For

• Affirming the consequent: All A are B. X is B. Therefore X is A. (INVALID)
• Undistributed middle: All A are C. All B are C. Therefore all A are B. (INVALID)
• Two particular premises: Some A are B. Some B are C. Therefore some A are C. (INVALID — the "some" subsets may not overlap)

Contrapositive Rule

"All A are B" is equivalent to "If not B, then not A." This is the only valid reversal.

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Strategy

• Spend no more than 60 seconds per syllogism
• If stuck, test the answer options against a quick Venn diagram
• Flag and move on if you cannot solve within the time limit

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Practice

Complete the 10 assessment questions for this lesson. Each presents premises and asks you to identify what validly follows or whether a given conclusion is valid.