FREE LESSON · Thinking Skills Foundations
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An assumption is the missing step between the reason and the conclusion. The argument needs it but never says it.
Assumption questions ask what an argument needs but doesn't say. The trap is picking something the argument already says. The assumption is the missing idea. It has to be true for the reason to lead to the conclusion.
Every argument gives a reason and a conclusion. Often a step is left out. That missing step is the assumption: an idea the writer needs but doesn't say. 'Turf never needs mowing, so the school will save money' skips a step. It assumes turf doesn't cost more in other ways. Your job is to find that hidden step.
Find the gap first. Read the reason, then the conclusion. Ask: what has to be true to get from one to the other? The assumption is in that gap. It isn't the reason the writer gives. It's the quiet idea the argument stands on.
Check it with the 'what if it's false?' test. Pretend your answer is false. If the argument falls apart, you've found the assumption. If the argument still works, it wasn't needed, so it isn't the answer.
The most tempting wrong answer repeats a reason the argument already gives. Another trap is a fact that's true but not needed. Neither is an assumption. Keep only the unsaid idea that, if false, brings the argument down.
In the turf argument, no mowing really does save money. But the conclusion is about all the money the school spends. Putting in, cleaning and replacing turf could cost more than mowing. So the hidden assumption is that those turf costs are smaller than the mowing saved. If they're bigger, the school doesn't save money, even though turf never needs mowing.
Assumption
an idea an argument needs but never says.It is never written down, only relied on.Evidence and conclusion
the reason the argument gives, and the claim it supports.The assumption bridges the gap between them.Negation test
suppose the assumption is false and see what happens.If the argument collapses, the assumption is real.Already-said trap
naming a written reason as if it were the assumption.If the argument already says it, it can't be the hidden assumption.The moveFind the gap between the reason and the conclusion. Fill it with the missing idea. Then cross out anything the argument already says.
show
Watch how a strong thinker proves the answer, one step at a time.
Read the problem, then follow the steps. You'll see the answer, the trap, and what to do next time.
Full problem: find the hidden step
Question: Which of these is an assumption the argument depends on?The Oval
A parent writes to the school newsletter:
'The school should replace the grass oval with artificial turf. Artificial turf never needs mowing, so over time the school would save money.'
Which idea does the argument need, but never say?
AThe turf's added costs will be less than the mowing costs saved.
BArtificial turf never needs mowing.
CEvery pupil would prefer turf to grass.
DThe school owns a mower already.
Work out what kind of answer you need.
The question asks for an assumption: an idea the argument needs but never says. So I find the gap between the reason ('never needs mowing') and the conclusion ('saves money'). Then I name the missing idea that fills it.
Follow the steps from the facts to the answer.
Find the gap, then fill it.
See why a tempting answer is wrong.
Common wrong answer: 'The argument assumes that artificial turf never needs mowing.'
Why it tempts you: it sounds important and uses the same words.
Why it's wrong: the argument already says it. An assumption is something the argument doesn't say.
Fix: the argument assumes turf's own costs are less than the mowing money it saves.
Say the answer and the shortest proof.
A. The argument assumes turf's own costs (putting it in, cleaning it, replacing it) are less than the mowing money saved. The argument jumps from 'never needs mowing' to 'saves money'. That jump only works if turf doesn't cost more in other ways.
What to remember for questions like this.
An assumption fills the gap between the reason and the conclusion. Here the gap is about total cost. The argument gives one saving, no mowing, and concludes the school saves money overall. That only works if turf doesn't bring bigger costs of its own. Test it: pretend turf costs far more than mowing ever did. Now the conclusion is false, even though 'never needs mowing' is still true. Something the argument already says is never the assumption.
What to do on your next question.
| In this question | Next time | Why it helps |
|---|---|---|
| Found the missing cost step. | Write reason → ? → conclusion before reading the answers. | The ? shows the idea the argument needs but doesn't say. |
| Pretended the cost idea was false, and the argument fell apart. | Try the 'what if it's false?' test on each strong answer. | A real assumption holds the argument up. |
| Crossed out 'never needs mowing' because it was already said. | Cross out anything the argument already says. | This avoids the most common trap. |
compare
The difference between what the argument says and what it silently needs.
Two students answered the same question. One followed the facts all the way. The other didn't.
The whole response
Already said
The argument assumes more bike racks would mean more students ride to school.
The hidden assumption
The argument assumes the new riders would otherwise have come by car. If they used to walk, there would be no fewer cars.
guide
One small step with help before you go solo.
Look back at the worked problem. Now try one like it.
A school says it will save money by using an app instead of paper notices. It won't have to pay for printing. What cost idea does this need, but never say? Then pretend your idea is false. Does the school still save money?
Want feedback on your own answer? Get started to practise with instant marking.
A school says replacing printed notices with an app will save money because printing costs will disappear. Which assumption is needed?
A council says its new bus route will shorten every pupil's trip because it passes the school. Which assumption does that claim need?
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