The art of thinking · 6 · Judgment, action and error
Slips, lapses and mistakes
Also known as: Error types (James Reason), Action slips, Generic error-modelling system (GEMS)
In human error research, James Reason distinguishes slips (an intended action carried out wrongly), lapses (a step forgotten or a memory failure) and mistakes (an action carried out as planned, but the plan itself is wrong, either rule-based or knowledge-based); violations, deliberate deviations from rules, are treated as a separate category.
- Cognitive psychology
- Human factors
- Safety
In one sentence
Reason’s error types: slips (wrong execution), lapses (memory failures), rule- and knowledge-based mistakes (wrong plans); violations apart (1990).
Example
Pressing “Start” instead of “Reset” on the next button is a slip; forgetting to close the bleed valve is a lapse; following the restart procedure for the wrong fault is a rule-based mistake.
What the research shows
Donald A. Norman (1981) classified action slips — errors in carrying out an intention — by their origin, for example capture errors, in which a frequent action sequence takes over from the intended one. James Reason (1990) combined this work with Jens Rasmussen's skill-, rule- and knowledge-based levels in his generic error-modelling system (GEMS): slips and lapses occur at the skill-based level, when attention or memory fails during routine actions; rule-based mistakes apply a wrong rule or a good rule in the wrong situation; knowledge-based mistakes arise from incomplete knowledge or a wrong mental model in new situations. Reason treated violations — deliberate deviations from procedures — as a separate category with different causes, and later described accidents as resulting from latent conditions in organizations as well as from active failures.
Evidence status
The classification is widely used in safety science, human reliability analysis and incident investigation, and by regulators as a way to describe types of human failure. It is a descriptive taxonomy derived from error diaries, incident reports and theory; assigning a real error to one type requires knowing the person's intention, which is often uncertain. Later work, for example in resilience engineering, criticizes the focus on individual errors and stresses that error categories are judgments made after the event.
How it applies
Different error types call for different information: slips and lapses are reduced by cues, checks and confirmation at the point of action, mistakes by better rules, diagnosis aids and concept information. The glossary “Applied cognitive psychology for information use” covers the design side, for example checklists and resumption lag. Human error is the broader safety term in the machine safety glossary; documentation alone does not control human error — it is addressed in the risk assessment through design and protective measures first.
External references
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Entries, context cards and transitional topics
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