Assumptions
Master the skill of identifying hidden premises that arguments rely upon but do not explicitly state.
Key Terms
What is an Assumption?
Arguments often rely on unstated premises — ideas taken for granted that are necessary for the argument to work. Identifying assumptions is crucial in critical thinking because they represent potential weak points in reasoning. If an assumption is false, the argument fails even if all stated reasons are true.
To find assumptions, look at the gap between the reasons and the conclusion. Ask: "What must be true for the reasons to support the conclusion?"
Maria has studied for 10 hours. Therefore, Maria will pass her exam.
Analysis: Assumptions include: studying for 10 hours is sufficient to pass; Maria studied the right material; the exam tests what she studied; she is not ill on the day. The argument assumes studying automatically leads to passing.
The Negation Test
A reliable way to test if something is a necessary assumption: negate it (make it false) and see if the argument collapses. If negating the statement destroys the argument, it is a necessary assumption. If the argument still works without it, it is not a necessary assumption.
This technique is highly valued in Cambridge examinations.
Argument: We should build more cycle lanes because cycling reduces obesity. Proposed assumption: "Cycle lanes will lead to more people cycling." Negation: "Cycle lanes will NOT lead to more people cycling."
Analysis: If cycle lanes do not increase cycling, the reason (cycling reduces obesity) cannot support the conclusion (build more cycle lanes). The negation destroys the argument — confirming this IS a necessary assumption.
Types of Assumptions
Value assumptions accept certain moral or ethical principles without question ("human suffering should be minimised"). Factual assumptions treat unverified claims as true ("the majority of the public would support this policy"). Definitional assumptions accept particular meanings of key terms. Causal assumptions accept that one thing leads to another without proof.
We should redistribute wealth from the rich to the poor. [Assumes: reducing inequality is a moral good worth pursuing.]
Analysis: The argument assumes that equality has moral value — a value assumption. Someone who does not share this value may reject the conclusion despite accepting the reasoning.
Cambridge Exam Tips
- 💡Use the negation test: if making the assumption false destroys the argument, it is a necessary assumption.
- 💡Assumptions are not stated in the passage — if you can quote it directly, it is a stated reason, not an assumption.
- 💡A good assumption bridges the gap between a specific reason and the conclusion. It should be as precise as possible.
- 💡In extended questions, explain WHY each assumption is needed — do not just list them.
Practice Questions
All practice →Identify two assumptions that this argument relies on and apply the negation test to each.
Answer in Practice →