A syllogism question gives two or three short statements built from All, Some and No and asks which conclusions follow. The statements may sound silly on purpose: you must assume they are true and judge only what the words force. This lesson covers the four statement types, Venn diagrams that test every case, the conclusion each pair of statements gives, three-statement chains, possibility conclusions and when 'either I or II' is right.
Assume every statement is true, however odd it sounds, and judge only what the words force. Real-world knowledge is the enemy here: if the statements say all rivers are chairs, then all rivers are chairs.
A conclusion follows only if it holds in every picture that obeys the statements. So draw one picture, then try to draw a second that obeys the statements but breaks the conclusion. If you can, it does not follow.
There are exactly four: All X are Y, Some X are Y, No X is Y, and Some X are not Y. Every statement and conclusion in this chapter is one of them, or a possibility built from one.
Statement
What it says
Reverses to
All X are Y
Every X is inside Y
Only "Some Y are X"
Some X are Y
At least one X is a Y, and "all" is not ruled out
"Some Y are X"
No X is Y
X and Y share nothing
"No Y is X"
Some X are not Y
At least one X is outside Y
Nothing
Two conventions
"Some" means at least one, and it allows all. So "Some pens are books" never tells you that some pens are not books.
Every group mentioned has at least one member. That is why "All pens are books" gives "Some books are pens".
Draw one circle per group, place them to obey every statement, then try to build a second picture that also obeys them but breaks the conclusion. The overlap in "Some X are Y" might be tiny or might swallow all of X; in "All X are Y", Y might be far bigger than X or exactly the same size.
A star marks a region that must have a member. A question mark marks one that may or may not.
Example 1 · A nested chain
All pens are books. All books are desks. Conclusions: I. All pens are desks. II. All desks are pens. Which follow?
The circles nest, pens inside books inside desks, so every pen is a desk: I follows.
The desk circle may be far bigger than the pen circle, so II does not follow. What does follow is "Some desks are pens".
Answer
Only I follows
Every pen is a desk, but the desks circle has room for desks that are not pens.
When two statements share a middle group B, the pair gives a fixed result. Learn the table and most two-statement questions take seconds.
First
Second
Definite conclusion about X and Y
All X are B
All B are Y
All X are Y, and Some Y are X
All X are B
No B is Y
No X is Y
Some X are B
All B are Y
Some X are Y
Some X are B
No B is Y
Some X are not Y, this direction only
No X is B
All B are Y
Some Y are not X, this direction only
No X is B
Some B are Y
Some Y are not X, this direction only
All B are X
All B are Y
Some X are Y
All B are X
No B is Y
Some X are not Y
All X are B
Some B are Y
Nothing
Some X are B
Some B are Y
Nothing
No X is B
No B is Y
Nothing
All X are B
All Y are B
Nothing
Exam shortcut
A definite conclusion needs the middle group fully covered at least once, by an "All B" or a "No". Two Somes, or an All that only points into B, leave the middle loose. With "Some … not", the useful case is All B are X plus Some B are not Y, which gives Some X are not Y.
Example 2 · Some and No
Some clocks are keys. No key is a card. Conclusions: I. Some clocks are not cards. II. Some cards are not clocks. Which follow?
The clocks that are keys cannot be cards, so I follows.
For II, draw every card inside the clock circle, away from the keys. Every statement still holds, and every card is a clock, so II does not follow.
Answer
Only I follows
The "some … not" runs from the group in the "Some" statement, clocks, never the other way.
Combine two statements at a time: join the first two with the table, then join the result with the third. If a link is loose, the chain breaks there, and nothing is certain beyond it.
Example 3 · A chain of three
Some chalks are crayons. All crayons are paints. No paint is a brush. What follows about chalks and brushes?
All crayons are paints, and no paint is a brush: no crayon is a brush.
Some chalks are crayons, and no crayon is a brush: some chalks are not brushes.
"No chalk is a brush" does not follow, since chalks that are not crayons may be brushes. Nor does the reversed "Some brushes are not chalks".
A possibility follows if at least one picture that obeys every statement makes it true. It fails only when it clashes with something definite. And whatever must be true can be true, so a certain fact is also a possibility.
If "No X is Y" is definite, "Some X being Y" and "All X being Y" are impossible.
If "Some X are not Y" is definite, "All X being Y" is impossible.
If "Some X are Y" is definite, "No X being Y" is impossible.
If "All X are Y" is definite, "Some X not being Y" is impossible.
Otherwise the possibility follows.
Example 4 · Possibilities
No shoe is a sock. Some socks are gloves. Conclusions: I. All gloves being shoes is a possibility. II. Some shoes being gloves is a possibility. Which follow?
The gloves that are socks can never be shoes, so "Some gloves are not shoes" is definite, which rules out I.
Gloves that are not socks are free, so a picture where some of them are shoes obeys everything. II follows.
Answer
Only II follows
Exam shortcut
"All X are Y" always allows "All Y being X", since the circles may be the same size. And groups linked only by a loose chain can have any relation.
Only when neither conclusion follows alone, both are about the same two groups, and they form a complementary pair, so exactly one of them is true in every picture.
Pair
Why exactly one is true
Some X are Y / No X is Y
The circles either meet or do not
All X are Y / Some X are not Y
Every X is inside Y, or at least one is outside
Example 5 · Either-or
All bats are rackets. Some rackets are balls. Conclusions: I. Some bats are balls. II. No bat is a ball. Which follow?
All plus Some gives nothing, so neither conclusion is definite.
Both are about bats and balls, and Some / No is a complementary pair.
Answer
Either I or II follows
Watch out
All / No looks opposite but is not complementary: both are false when X partly overlaps Y. Some / Some-not can both be true. Neither pair ever gives "either". And if one of a complementary pair does follow, the answer is "only I", not "either".
Statements: All spoons are plates. All plates are cups.
Conclusions:
I. All spoons are cups.
II. All cups are spoons.
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AnswerA · Only I follows
Every spoon is a plate and every plate is a cup, so every spoon is a cup. Conclusion I follows.
Conclusion II turns 'All spoons are cups' around. The cup circle may be much bigger than the spoon circle, so there can be cups that are not spoons. II does not follow.
Only I follows.
Worth noting
'All' is not reversible. From 'All X are Y' you may say 'Some Y are X', never 'All Y are X'.
Statements: All candles are lamps. No lamp is a chair.
Conclusions:
I. No candle is a chair.
II. No chair is a candle.
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AnswerD · Both I and II follow
The candle circle sits inside the lamp circle, and the lamp circle is separate from the chair circle. So no candle can be a chair: conclusion I follows.
'No' is reversible: 'No candle is a chair' says exactly the same as 'No chair is a candle'. Conclusion II follows too.
Read the statements as true, even if they conflict with commonly known facts, and decide which of the conclusions follows.
Statements: All roses are flowers. Some flowers fade quickly.
Conclusions: I. Some roses fade quickly. II. All flowers are roses.
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AnswerD · Neither conclusion follows
The flowers that fade quickly are only some of the flowers. Nothing says roses are among them, so conclusion I is possible but not certain.
Conclusion II reverses the first statement. 'All roses are flowers' allows plenty of flowers that are not roses, so it does not follow either.
Neither conclusion is forced by the statements.
Worth noting
A conclusion 'follows' only if it must be true whenever the statements are. Something that merely could be true is not enough, and that is what makes conclusion I fail.
Statements: All drums are bells. Some bells are whistles.
Conclusions:
I. Some drums are whistles.
II. No drum is a whistle.
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AnswerC · Either I or II follows
The drum circle is inside the bell circle; the whistle circle overlaps the bell circle somewhere.
The overlap may pass through the drum circle (then some drums are whistles) or miss it entirely (then no drum is a whistle). Neither conclusion is definite on its own.
The two conclusions are about the same pair, drums and whistles, and 'Some … are' and 'No … is' are opposites: exactly one of them must be true.
So either I or II follows.
Worth noting
'All + Some' gives no definite conclusion. When neither follows, check whether the pair is a complementary Some/No pair before choosing 'Neither'.
Statements: All buttons are coins. No coin is a ring.
Conclusions:
I. No button is a ring.
II. Some rings are buttons.
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AnswerA · Only I follows
Every button is a coin, and no coin is a ring, so no button can be a ring. Conclusion I follows.
Conclusion II says the opposite of I. Since I is definite, II is definitely false.
Only I follows.
Worth noting
The pair 'No button is a ring / Some rings are buttons' looks like an either-or pair, but either-or needs NEITHER to follow alone. Here I follows, so the answer is 'Only I'.
Statements: No tent is a pillow. Some pillows are blankets.
Conclusions:
I. Some tents are not blankets.
II. Some blankets are not tents.
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AnswerB · Only II follows
The blankets that are pillows cannot be tents, because no pillow is a tent. So some blankets are not tents: II follows.
For conclusion I, draw all the tents inside the blanket circle but away from the pillows. Every statement still holds, yet every tent is a blanket. So I is not definite.
Only II follows.
Worth noting
In 'No + Some' the definite conclusion runs from the SECOND group: Some blankets are not tents. Reading it the other way round is the classic trap.
Statements: All violins are flutes. All violins are sitars.
Conclusions:
I. Some flutes are sitars.
II. Some sitars are violins.
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AnswerD · Both I and II follow
Violins exist (every category is non-empty), and each violin is both a flute and a sitar. So some flutes are sitars: I follows.
Every violin is a sitar, so at least some sitars are violins: II follows.
Both I and II follow.
Worth noting
When the SUBJECT is shared ('All V are F, all V are S'), the Vs themselves sit in both groups, so 'Some F are S' is certain. Compare with a shared predicate, which gives nothing.
Statements: Some blankets are quilts. Some blankets are not quilts.
Conclusions:
I. Some quilts are not blankets.
II. All quilts are blankets.
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AnswerC · Either I or II follows
The statements only say the blanket circle is partly inside and partly outside the quilt circle. The quilt circle may lie wholly inside the blankets or may stick out.
So neither 'Some quilts are not blankets' nor 'All quilts are blankets' is definite.
They share the same subject and predicate (quilts, blankets) and form the complementary All / Some-not pair: one of them must be true.
Either I or II follows.
Worth noting
The complementary pairs are Some/No and All/Some-not, on the same two groups. All/Some-not is the one students forget.
Statements: All feathers are balloons. Some feathers are not lanterns.
Conclusions:
I. Some balloons are not lanterns.
II. Some lanterns are not balloons.
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AnswerA · Only I follows
Pick a feather that is not a lantern. It is a feather, so it is also a balloon. That balloon is not a lantern, so some balloons are not lanterns: I follows.
For II, draw the lantern circle entirely inside the balloon circle (away from that feather). All statements hold and every lantern is a balloon, so II is not definite.
Only I follows.
Worth noting
'Some X are not Y' cannot be reversed into 'Some Y are not X'. Conclusion II is exactly that reversed form.
Statements: Some benches are not tables. All tables are stools.
Conclusions:
I. Some benches are not stools.
II. Some stools are not benches.
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AnswerC · Neither I nor II follows
The benches that are not tables may still be stools (the stool circle is bigger than the table circle). Draw every bench inside the stool circle: the statements hold, so I is not definite.
Now draw the stool circle (with the table circle inside it) entirely inside the bench circle, leaving some benches outside the tables. The statements hold and every stool is a bench, so II is not definite either.
The two conclusions are about different subjects (benches in I, stools in II), so they cannot be an either-or pair.
Neither I nor II follows.
Worth noting
A 'Some … not' statement gives nothing when it meets an All that runs away from it. Also, Some-not / Some-not is never an either-or pair.
Statements: All shirts are jackets. No jacket is a coat. Some coats are sweaters.
Conclusions:
I. Some sweaters are not shirts.
II. No shirt is a sweater.
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AnswerA · Only I follows
Every shirt is a jacket and no jacket is a coat, so no shirt is a coat.
The sweaters that are coats are therefore not shirts. Some sweaters are not shirts: I follows.
Sweaters that are not coats are unrestricted and may be shirts, so 'No shirt is a sweater' is not definite. II does not follow.
Only I follows.
Worth noting
First combine the first two statements (No shirt is a coat), then join that with the third. Joining 'No + Some' gives a Some-not starting from the Some group.
Statements: Some lamps are torches. No torch is a candle. All candles are lanterns.
Conclusions:
I. Some lanterns are not torches.
II. Some lamps are not candles.
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AnswerD · Both I and II follow
Candles exist, every candle is a lantern, and no candle is a torch. So those lanterns are not torches: I follows.
The lamps that are torches cannot be candles. So some lamps are not candles: II follows.
Both I and II follow.
Worth noting
The 'No' in the middle pays off twice: through the candles (an All link) it gives 'Some lanterns are not torches', and through the lamps (a Some link) it gives 'Some lamps are not candles'.
Statements: Some trunks are chests. All chests are crates. No crate is a barrel.
Which one of the following conclusions definitely follows?
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AnswerC · Some trunks are not barrels
Every chest is a crate and no crate is a barrel, so no chest is a barrel.
The trunks that are chests are therefore not barrels: some trunks are not barrels. This follows.
Trunks that are not chests may be barrels, so 'No trunk is a barrel' is not certain. 'Some barrels are chests' contradicts 'No chest is a barrel'. 'All crates are chests' reverses an All.
The conclusion that definitely follows is: Some trunks are not barrels.
Worth noting
Upgrading the Some-not to a full 'No trunk is a barrel' is the tempting mistake.
Statements: All buckets are tubs. Some tubs are basins.
Conclusions:
I. All tubs being buckets is a possibility.
II. Some buckets being basins is a possibility.
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AnswerD · Both I and II follow
A possibility follows if at least one picture that obeys the statements makes it true.
Draw the bucket circle and the tub circle as the same circle, with the basins overlapping it. Every statement holds and all tubs are buckets, so I follows.
Draw the basin overlap passing through the buckets. The statements still hold and some buckets are basins, so II follows.
Both I and II follow.
Worth noting
Nothing in the statements forbids either picture. For a possibility, you only need ONE valid picture, not every picture.
Statements: All poles are posts. All posts are pillars.
Conclusions:
I. All pillars being poles is a possibility.
II. Some poles not being pillars is a possibility.
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AnswerA · Only I follows
All three circles may coincide: every pillar a post, every post a pole. That picture obeys both statements, so I follows.
Every pole is a post and every post is a pillar, so every pole is a pillar in every picture. 'Some poles not being pillars' is impossible: II does not follow.
Only I follows.
Worth noting
'All A are B' allows A and B to be exactly the same group, so 'All B being A' is always a possibility.
Statements: All carrots are radishes. No radish is a beet.
Conclusions:
I. Some carrots being beets is a possibility.
II. All beets being radishes is a possibility.
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AnswerC · Neither I nor II follows
Every carrot is a radish and no radish is a beet, so no carrot is a beet is definite. 'Some carrots being beets' clashes with it, so I does not follow.
No radish is a beet, so the beets can never be radishes. 'All beets being radishes' is impossible, so II does not follow.
Neither I nor II follows.
Worth noting
A possibility needs just one valid picture, but when a 'No' statement separates two groups there is no picture where they meet.
Statements: No cloud is a star. Some stars are moons. All moons are planets.
Conclusions:
I. All moons being clouds is a possibility.
II. Some planets being clouds is a possibility.
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AnswerB · Only II follows
Some moons are stars, and no star is a cloud, so those moons can never be clouds. 'All moons being clouds' is impossible: I does not follow.
Planets that are not moons (or moons that are not stars) are unrestricted, so a picture where some planets are clouds obeys every statement. II follows.
Statements: Some sofas are not beds. All beds are cots.
Conclusions:
I. All sofas being cots is a possibility.
II. All cots being sofas is a possibility.
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AnswerD · Both I and II follow
For I, draw every sofa inside the cot circle, with some sofas in the part that is not beds. Every statement holds, so I follows.
For II, draw the cot circle (with the bed circle inside it) inside a bigger sofa circle, leaving some sofas outside the beds. Every statement holds, so II follows.
Both pictures are valid, so both possibilities follow.
Both I and II follow.
Worth noting
The only fixed fact is that at least one sofa is not a bed. Both pictures keep such a sofa, so neither breaks the statements.
Statements: Some sheds are huts. All huts are cabins. No cabin is a villa.
Conclusions:
I. Some sheds being villas is a possibility.
II. All sheds being villas is a possibility.
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AnswerA · Only I follows
Every hut is a cabin and no cabin is a villa, so no hut is a villa. The sheds that are huts are therefore not villas, so 'Some sheds are not villas' is definite.
That makes 'All sheds being villas' impossible: II does not follow.
Sheds that are not huts are unrestricted, so a picture where some of them are villas obeys every statement. I follows.
Only I follows.
Worth noting
Find the definite Some-not first. Any possibility that contradicts it is out.
Statements: Some tulips are orchids. Some orchids are irises.
Conclusions:
I. All tulips are irises.
II. No tulip is an iris.
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AnswerC · Neither I nor II follows
Two 'Some' statements give no definite link between tulips and irises, so neither I nor II follows alone.
'All' and 'No' are not a complementary pair: the picture where some tulips are irises and some are not makes both I and II false.
Since it is possible for both to be false, 'either I or II' is not guaranteed.
Neither I nor II follows.
Worth noting
All/No is not an either-or pair because both can be false at once: if some tulips are irises and some are not, neither 'All tulips are irises' nor 'No tulip is an iris' is true. The complementary pairs are Some/No and All/Some-not.
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