How Do I Know That?

Tufte has ended his Microsoft Machine Learning Summit keynote, and many others, with three questions he asks in every context where evidence informs decisions: How do I know that? How do you know that? How do they know that? Three sentences. Three applications of the lie-factor principle extended into epistemic hygiene. The questions are beautiful in their economy — no unnecessary words, no decoration, no evasion. Just the demand: show me the evidence. Show me the evidence that this output is trustworthy. Show me the evidence that this code is sound. Show me the evidence that this conclusion follows from these premises. Tufte's July 2025 response to a physician's post about Microsoft's medical AI demonstrated the discipline in practice: he asked whether other datasets had been examined but left unpublished, noted that the accompanying graphic required memorizing a complex color code, and invoked the observation by former editors of the New England Journal of Medicine and The Lancet that