Assumptions: The Hidden Premises

Every argument relies on assumptions — unstated beliefs that must be true for the argument to work. Identifying assumptions is one of the most commonly tested skills on the LNAT, and one of the most challenging. This lesson teaches you what assumptions are, how to find them, and the critical distinction between necessary and sufficient assumptions.

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What is an Assumption?

An assumption is an unstated premise that the argument depends upon. It is a belief the author takes for granted without explicitly stating it.

Think of an argument as a bridge between premises and conclusion. The stated premises are the visible supports. Assumptions are the hidden supports — if you remove them, the bridge collapses.

Formal Definition: An assumption is a statement that is not explicitly made in the argument but must be true for the conclusion to follow from the premises.

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A Simple Example

"James has lived in France for ten years, so he must speak French fluently."