How a language model works, in 90 seconds
A language model predicts the next word. That's the whole mechanism. It was trained on a large slice of human text, and it writes the most plausible continuation of whatever you give it.
Plausible is not the same as true. The model has no database it looks things up in. It has no flag that says "I'm guessing now." When it knows a topic well, plausible and true overlap. When it doesn't, it produces fluent, formatted, confident text that is wrong.
Two consequences matter for your work:
- Closed-book vs open-book. Ask the model a question from memory and it's closed-book: fluent, shaky on specifics. Paste your source document into the prompt and it's open-book: accuracy jumps. An accountant who pastes the actual IRS notice gets a far better summary than one who asks "what does IRS Notice 2024-XX say?"
- Training cutoff. The model learned from text up to a fixed date. It does not know this year's mileage rate, last month's bar opinion, or the funder deadline that moved.
Rule of thumb: supply the source whenever you can. When you can't, treat every specific claim as unverified.