How to Weigh in Debate
Use impact calculus to tell the judge why your argument matters more.
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How do you weigh arguments in a debate?
Compare your impact with your opponent's on a named measure and say why that measure matters. The six common measures are magnitude, probability, timeframe, reversibility, scope and link strength. Which one is strongest depends on the round, but probability and link strength often persuade more than magnitude, because every team claims its impact is huge. When their impact wins on one measure and yours on another, explain why your measure should count more here. Start weighing in your first speech and build on it in rebuttal, rather than saving it for the end.
Six ways to compare impacts
Magnitude, probability, timeframe, reversibility, scope and link strength, with when each one is the right comparison.
Weighing the weighing
What to say when your impact wins on one measure and theirs wins on another.
Weighing in every speech
Where weighing belongs in the constructive, the rebuttal and the final speech, so the judge never decides without it.
Why weighing wins rounds
Most rounds end with both sides holding some offence. When that happens, the judge needs a reason to prefer one impact over the other. Weighing gives that reason. Without it, the judge has to compare the impacts alone, and a judge left to decide will not always pick yours.
Weighing is also called impact calculus: comparing impacts on a set of measures to show which one should decide the round. The name differs between circuits; the skill is the same.
The six measures
- Magnitude: how big is the impact for the people it affects?
- Probability: how likely is it to happen at all?
- Timeframe: how soon does it happen, and does an earlier harm prevent or worsen a later one?
- Reversibility: can it be undone if we get it wrong?
- Scope: how many people does it reach, and who are they?
- Link strength: how certain is the causal chain from the motion to the impact?
Magnitude is the measure debaters reach for first and the one judges trust least, because every team claims its impact is huge. Probability and link strength often do more work, because they are about the argument the judge just heard rather than a prediction.
Compare, do not just describe
Saying your impact is large is description. Weighing is comparison: your impact against theirs, on a named measure, with a reason. A useful pattern has three parts:
- Name the measure: "Prefer our impact on probability."
- Compare directly: "Our harm is happening now, in every school that uses the policy; theirs depends on three things going wrong in sequence."
- Say why the measure matters: "A certain harm should outweigh a speculative one, because the judge cannot weigh what may never happen."
When their impact wins on one measure and yours on another, weigh the weighing. Explain why your measure should count more in this round, for example why an irreversible harm outweighs a larger reversible one.
Worked example
Motion: This house would ban fossil fuel advertising
Proposition impact: Advertising slows the shift away from fossil fuels, adding to long-term climate harm.
Opposition impact: A ban sets a precedent for restricting lawful speech, which governments can extend to other industries.
Weak weighing: "Climate change is the biggest problem humanity faces, so we win." Magnitude alone, with no comparison.
Strong weighing: "Even if the precedent concern is real, it is speculative: it needs future governments to choose to extend it. The climate harm is happening now and cannot be reversed. Prefer us on probability and reversibility."
The strong version concedes nothing it does not need to, names two measures and gives the judge a reason to use them.
When to weigh
Start in the constructive, so the judge hears your impact framed before the other side frames theirs. Reinforce it in rebuttal, where you compare each clash as you win it. Make it the centre of the final speech. Late weighing is better than none, but weighing that only appears at the end competes with a decision the judge has already begun to make.
In Public Forum, weighing should be in summary if you want it in final focus. In Lincoln-Douglas, weighing usually runs through the value and criterion. In World Schools, third speakers weigh the clashes and the reply speech weighs the whole debate. British Parliamentary has no reply speech, so the whips weigh the whole debate.
Practise weighing with DebateLab
Run a Sparring round and read the verdict: it says which arguments decided the round and why, which shows whether your weighing changed the outcome. Ask the coach to compare two impacts on a named measure, then write your own version and say it against the timer.
Frequently asked questions
What is weighing in debate?
Comparing your impact with your opponent's to show the judge why yours should decide the round, using measures such as magnitude, probability, timeframe, reversibility, scope and link strength.
Is impact calculus the same as weighing?
Yes. Impact calculus is another name for weighing, used more often in American formats such as Policy and Public Forum.
Which weighing measure is strongest?
It depends on the round. Probability and link strength are often more persuasive than magnitude, because they compare the arguments the judge actually heard.
What if my impact loses on magnitude?
Weigh on a different measure and say why that measure matters more here, for example that your harm is certain and theirs is speculative.
When should I start weighing?
In the first speech. Early weighing frames the round; weighing that appears only in the final speech competes with a decision already forming.