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In this lesson, we’ll explore a hidden but powerful part of many arguments: unstated assumptions. These are the ideas that authors don’t say out loud—but still expect you to accept in order for their argument to make sense.
You’ll learn how to spot these “missing steps” in reasoning and understand why they matter. Identifying assumptions is a key skill in critical thinking because it helps you analyze how arguments are built and whether they truly hold up under scrutiny.
By the end of this lesson, you’ll be able to uncover the unstated assumptions behind a claim and explain how they affect the strength of an argument.
An unstated assumption is a hidden step in reasoning—something the author expects you to accept without saying it directly. It acts like a missing link between the reasons and the conclusion. Without it, the argument wouldn’t make sense.
‘You had better watch out – there’s a bear behind you!’
This only makes sense if we assume:
The bear is real.
The bear is dangerous.
The bear is close enough to be a threat.
These assumptions aren’t stated, but they’re what make the warning meaningful.
Another example:
Liv wants to go to university; therefore, she should work hard at school.
At first, this might seem complete. But the argument only works if we assume something like:
Working hard at school improves your chances of getting into university.
That’s the unstated assumption—it’s not written, but it’s necessary for the conclusion to follow.
We can also test assumptions using the negative test: try reversing the assumption. If the argument falls apart, then the assumption is essential.
For example: If working hard didn’t help you get into university, would the conclusion, ‘Liv should work hard at school’ still make sense?
No—so the assumption is clearly needed.
Practice
Practice
Identify the unstated assumption in each short argument.
Raj wants to audition for a local band. He plays guitar but is also a good drummer. The band plays gigs all over the city and therefore Raj would need a car to transport his drumkit around with him to gigs. Raj does not have enough money to buy a car and consequently it might be better if he auditioned on guitar.
The traffic is always heavy on Monday mornings. It is very important that you get to college on time. You should catch an earlier bus than usual.
Smoking is a major cause of illness and a considerable drain on the health service's resources. Recent figures show that the number of people giving up smoking has increased, so there will be less strain on the health service. The money saved can be used to improve preventive treatments.
There appear to be growing concerns about the number of 6- and 7-year-olds who are unable to read. However, there is no reason for this to be a problem. Every child has to go to school and is taught by a qualified teacher. Even if this does not work - and apparently it does not always - there are many libraries in our cities, with specialist advisers running after-school reading clubs and book groups, all designed to help young children read.
Rugby is a much more exciting game to watch than football. Unlike football, it has complex rules and tactics that create many more possibilities, both in attack and defense. Football has much simpler rules and tactics and will never be anything other than boring to watch.
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