Insufficient but Necessary part of an Unnecessary but Sufficient condition
Updated 2026-08-09
INTRODUCTION
English translation pending.
CORE DEFINITION
The INUS condition is an analysis of causation proposed by the philosopher J. L. Mackie. A cause, on this account, is an insufficient but non-redundant part of an unnecessary but sufficient condition. In plain terms: some set of conditions is jointly sufficient to produce the effect; the cause is one member of that set that is necessary for the set to work; and other sets could have produced the same effect, so no single set is necessary. The analysis explains why causes are usually components of a conjunction rather than single sufficient triggers, and it handles cases of overdetermination where several paths lead to one outcome.
SCAFFOLDING EFFECT
Reduce cognitive load
- Use condition sets: list the full conjunction of conditions that together produced the outcome. - Use necessity test: remove the candidate cause from the set and ask whether the effect still occurs. - Use alternative paths: identify other sufficient sets, which is what makes the cause unnecessary.
Anchor fast decisions
Most real outcomes have multiple contributing conditions and more than one possible route, so naming a single cause misrepresents the structure. Specifying a sufficient set makes the conjunction explicit, and testing each member for necessity within that set identifies which one does the work. Enumerating alternative sets establishes that no single set was required, which explains why the same effect can arise in different ways. The analysis prevents two opposite errors: naming a contributor as the sole cause, and concluding nothing is a cause.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Necessity_and_sufficiencyverified
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