The Source Ladder.
The Source Ladder is a five-rung way to check a source: rank it by how close it sits to the original. Rung 1 is the primary source itself, the law or the filing or the dataset. Rung 5 is pure speculation. When an answer matters, push yourself, and the AI, up the ladder toward rung 1. It is a filter, not a law. Here is the ladder, and a real case of it catching a slip.
// Higher on the ladder = closer to the original
- 1 Primary source
The original itself. The law, the filing, the dataset, the person who was there.
e.g. The gov.uk page that sets the fine.
- 2 Official source
The body responsible, restating its own original.
e.g. A regulator or department summarising its own rule.
- 3 Reputable secondary
A trusted outlet reporting the original honestly.
e.g. An established news site, or a known reference site.
- 4 Forum or summary
Second-hand and unchecked. A comment, a blog, a quick AI overview with no link.
e.g. A Reddit answer, or an AI summary that cites nothing.
- 5 Pure speculation
A guess dressed as fact, with nothing behind it.
e.g. “Someone said”, a made-up figure, a confident hunch.
You will not always reach rung 1, and you do not need to for a trivial question. The point is simple: the more a claim can cost you if it is wrong, the higher up the ladder you should insist on standing before you trust it.
The ladder, catching one.
The maximum UK fine for using a handheld phone while driving a lorry or bus is £2,500.
Gemini got the number right. That fine is published on gov.uk, a rung-1 fact. Beside the figure it displayed a Police.uk source label, but the captured label exposed no destination URL. The correct gov.uk guide appeared only as a detached closing source. An opaque label has no rung because there is no page to inspect.
The danger is that an official-looking label can feel like a checked citation. The ladder catches it with one question: what exact page is this? If the answer exposes no page, stop there. If it does, climb to the most direct source and find the claim on it. Police.uk now carries the same figure, but the historical destination is unknown.
The full run: AI cites the wrong source (8 July 2026), where three of five assistants cited a real page that did not back their claim.
Cited rung 3, claimed rung 1.
That is how a catch or a logged failure records a slip like Gemini’s in one line. The claim was a rung-1 fact. The citation behind it was a rung-3 source dressed up as proof of it. The number sitting where the source should be tells you the exact size of the gap: a genuine primary source would read “claimed rung 1, cited rung 1”. When the two numbers diverge, that space between them is where a confident answer goes wrong.
A page can straddle rungs, so the shorthand is used only when the fit is clean. It is a way to see the gap, not a label to force onto every miss.
The ladder is the reader’s version of the source-tier grading the site already runs on the Scoreboard. For why we grade the way we do, see How we grade. For the two habits it sits alongside, asking well and checking well, see the method.