Syllogism
Syllogism is pure logic wearing a language costume — draw Venn diagrams and the trick options disappear. The exam's favourite failure mode is trusting real-world plausibility over what the statements actually say.
Mental model
Draw the circles — never argue in words. A conclusion is valid only if it holds in EVERY diagram the premises allow, not merely in the convenient one you drew first, so deliberately draw the awkward arrangement too. 'All A are B' is one circle inside another and does NOT let you reverse it to 'all B are A'. 'Some' never upgrades to 'all'. Two negative premises or two particular ('some') premises give no definite conclusion at all. When two conclusions each fail alone but together cover all cases, the answer is 'either-or'.
Associations
A short trigger on the left, everything it pulls with it on the right.
'All A are B' does not mean 'all B are A'.
'All cats are animals' is true, but 'all animals are cats' clearly is not. This single asymmetry — that a universal statement does not reverse — is the source of most wrong syllogism answers.
Draw the circles; ignore what you know about the real world.
Syllogism questions deliberately use statements that may be factually false ('all doctors are fish') to test whether you can reason from the given premises alone. Venn diagrams force this discipline because a diagram cannot smuggle in outside knowledge the way a gut feeling can.
Things to remember
The night-before list. Short enough to recall cold.
- 1A conclusion follows only if it is true in every possible diagram consistent with the given statements — if even one valid diagram breaks it, the conclusion does not follow.
- 2'Some A are B' only guarantees overlap, not that all A are B or that all B are A — draw the minimum required overlap, nothing more.
- 3'No A are B' means the two circles do not touch at all — a completely disjoint pair.
- 4When two conclusions are offered and each is possible in a different valid diagram but not both together, the standard answer is 'either follows' rather than both or neither.
In detail
- 'All A are B' allows 'some B are A' but never 'all B are A'.
- 'No A is B' converts fully: 'no B is A' is always valid.
- Two particular premises (both starting 'some') yield no valid conclusion; likewise two negative premises yield none.
- If one premise is negative the conclusion must be negative; if one premise is particular the conclusion must be particular.
- Answer only from the given premises, treating them as true even if they contradict real-world knowledge; importing outside facts is the standard trap.
Where people slip
- Never reject a conclusion because it sounds factually wrong. A syllogism is judged purely on logical validity given the stated premises.
Check yourself
Nothing here is scored — it will not change your mastery figures.
Statements: All pens are books. All books are tables. Conclusion: All pens are tables.
From the question bank
Statements: All cats are dogs. All dogs are horses. Conclusions: I. All cats are horses. II. Some horses are cats. Which conclusion(s) follow?
From the question bank
Statements: All pens are pencils. Some pencils are erasers. Conclusions: I. Some erasers are pens. II. Some pencils are pens. Which conclusion(s) follow?
Books to read
- A Modern Approach to Verbal and Non-Verbal Reasoning — R S Aggarwal
- Analytical Reasoning — M K Pandey
Official sources
Hand-checked official domains only — the notes above carry no links of their own.