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FLR·B·004

Mode Error

broke: visibility of system state documented

A mode is when the same action means different things depending on hidden state — and a mode error is the moment the human's model of that state and the machine's diverge. Caps Lock is the everyday specimen: the keyboard you're using is briefly not the keyboard you think you're using. The grave specimens live in aviation's human-factors literature, where decades of documented incidents trace to autoflight mode confusion — crews commanding one thing while the automation, legitimately and lethally, was in a state that heard another. That body of official reporting is why "mode awareness" is a certification topic and not a design nicety.

Software's daily mode errors are gentler but constant: typing into the wrong window, the vim novice's panic, the camera that was on video when you pressed for a photo, the message sent to the channel you forgot you'd switched to. The pattern is identical at every scale — state changed; the announcement didn't reach the human.

A a A CAPS — hidden state one key, two meanings — the mode decides, quietly
FIG B·004 — the smallest mode error, standing in for the largest.
The lessonModes are sometimes necessary; invisible modes never are. Every mode needs a persistent, glanceable announcement — and the more consequential the divergence, the louder the state must dress. The best fix is fewer modes; the honest fallback is modes that cannot be missed.
The recordNorman on modes (1988); aviation human-factors and accident-investigation literature on autoflight mode awareness (official reports; FAA/NTSB and international equivalents).
StairwellVisibility of system state — Nielsen's first heuristic, and the modal's namesake risk (Floor 3).
Upstairs kinFloor 1's Seven States — the discipline that makes state announce itself at the smallest grain.

Why documented: Mode error has a formal literature going back to Norman’s 1981 categorisation of slips.