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Recognising assumptions is one of the most distinctive question types in the UCAT Decision Making subtest. These questions test whether you can identify the unstated premises that an argument relies on — the hidden beliefs that must be true for the argument's conclusion to hold. This lesson explains what assumptions are, how they differ from stated premises, and why they matter in clinical reasoning.
An assumption is an unstated belief or premise that an argument takes for granted. It is the gap between the evidence presented and the conclusion drawn.
Statement: "We should hire Dr Okafor because she graduated top of her class."
Stated premise: Dr Okafor graduated top of her class.
Conclusion: We should hire Dr Okafor.
Assumption: Graduating top of one's class is a good indicator of being suitable for the job.
The argument only works if you accept this unstated link between academic performance and job suitability. If this assumption is false — if, for example, the job requires practical skills that are not measured by academic results — the argument collapses.
Every argument has three components:
| Component | Description | Stated or unstated? |
|---|---|---|
| Premises (evidence) | The facts or claims presented to support the conclusion | Stated |
| Conclusion | The point the argument is trying to establish | Usually stated |
| Assumptions | The unstated beliefs that connect the premises to the conclusion | Unstated |
Key Insight: Assumptions are the invisible glue holding an argument together. If you remove the assumption, the argument falls apart.
We make assumptions constantly without realising it. Consider:
"Take an umbrella — it is going to rain."
Assumptions include:
Each of these is taken for granted. If any one of them is false (e.g., you are staying indoors), the advice loses its justification.
The UCAT often uses medical or healthcare scenarios. Common clinical assumptions include:
| Argument | Hidden assumption |
|---|---|
| "The patient should start antibiotics because they have a bacterial infection." | Antibiotics are effective against this specific bacterial infection; the patient is not allergic. |
| "We should screen all patients over 50 for bowel cancer." | The screening test is sufficiently accurate; early detection improves outcomes; the benefits outweigh the risks and costs. |
| "This treatment reduced symptoms in a clinical trial, so we should use it in our hospital." | The trial population is comparable to our patients; the results will generalise. |
| Concept | Direction | Example |
|---|---|---|
| Assumption | Unstated premise that supports the conclusion | "Graduating top of class means she is a good hire" |
| Inference | A conclusion drawn from the evidence | "Dr Okafor will be a good hire" |
An assumption is something the argument needs to be true in order to work. An inference is something you conclude from the argument. In UCAT questions, you are typically asked to identify the assumption, not to make an inference.
The most reliable method for identifying assumptions is to look for the gap between the premises and the conclusion.
What is the argument trying to prove or recommend?
What evidence or reasons are explicitly given?
What must be true — but is NOT stated — for the conclusion to follow from the premises?
"The hospital should switch from Drug A to Drug B. Drug B has fewer side effects."
Conclusion: The hospital should switch to Drug B.
Stated premise: Drug B has fewer side effects.
Gap: The argument assumes that:
Any of these could be the "assumption" in a UCAT question.
These bridge the gap between the evidence and the conclusion.
"James should apply to medical school because he volunteers at a hospital."
Connecting assumption: Volunteering at a hospital is relevant to medical school applications (or demonstrates qualities that medical schools value).
These are basic facts about the world that the argument takes for granted.
"We should vaccinate children to prevent measles."
Background assumptions: Vaccines are effective; measles is harmful; children can be vaccinated safely.
These assume that what is true in one context applies more broadly.
"This treatment worked in a trial of 200 patients, so it will work for our patients."
Scope assumption: The trial patients are sufficiently similar to our patients for the results to generalise.
| Trap | Description | How to avoid |
|---|---|---|
| Selecting a stated premise | The option restates something already in the argument | Assumptions are UNSTATED — check that the option is not already in the text |
| Selecting an inference | The option is a conclusion you can draw, not an assumption you need | Assumptions are inputs to the argument, not outputs |
| Selecting something irrelevant | The option is true but not required by the argument | Use the negation test (covered in the next lesson) to check if the argument needs it |
| Selecting something too strong | The option goes beyond what the argument needs | Look for the most precise, minimal assumption |