Finding the Unstated Assumption

Identify the hidden link that must be true for an argument's evidence to support its claim.

Every argument rests on assumptions, often unstated, that connect evidence to claim. Logicians sometimes call this link the warrant. If the assumption is false, the argument fails even when every stated fact is true. To find it, ask: what must the writer believe for this evidence to prove this claim? Worked example: 'Sales of the new phone were the highest of any model this year, so it must be the best phone on the market. ' Stated evidence: highest sales. Claim: best phone. Hidden assumption: the most popular product is the best product.

Once stated, the assumption is easy to question; popularity can result from advertising, price, or brand loyalty rather than quality. Another example: 'Maya studied for ten hours, so she will ace the test. ' Hidden assumption: hours of study guarantee results. Stating assumptions aloud is one of the most powerful moves in critical reading, because weak arguments often depend on assumptions their authors hope you will not notice.

• 1An unstated assumption links evidence to claim.
• 2Ask what must be true for the evidence to prove the claim.
• 3Weak arguments often hide questionable assumptions.