Definition
A warrant is the logical link between evidence and a claim. It answers the question "why does that evidence prove this claim?" The term comes from the Toulmin model of argument, where a claim needs grounds (evidence) and a warrant (the reasoning that connects the grounds to the claim) to count as a complete argument rather than two disconnected statements.
Example
Claim: social media platforms should carry warning labels for teenagers. Evidence: a study found anxiety rates rose alongside social media adoption. On its own, that only shows correlation. The warrant closes the gap: algorithmic feeds are built to maximize engagement through social comparison, and social comparison is an established driver of anxiety in adolescents specifically. That sentence is the warrant, and it is what turns a statistic into an actual argument.
Common mistakes
The most common failure is skipping the warrant entirely and moving straight from evidence to claim, trusting the judge to supply the missing reasoning themselves. Judges should not have to do that work, and if they have to guess what you meant, they may guess wrong or credit your opponent's interpretation of the same evidence instead.