Conjoint Method
Updated 2026-08-22
INTRODUCTION
English translation pending.
CORE DEFINITION
The joint method of agreement and difference is one of John Stuart Mill's five methods of experimental inquiry, set out in A System of Logic. It first identifies a factor common to all instances where the phenomenon appears, then checks that the same factor is absent in instances where the phenomenon does not appear. The core proposition is that the two comparisons reinforce each other, so the inference is stronger than either agreement or difference alone. The key qualification is that a shared factor may still be a joint effect of a hidden common cause, so the method raises confidence without proving causation.
SCAFFOLDING EFFECT
Reduce cognitive load
- Compare Positive Cases: list occurrences of the phenomenon and extract the factors they all share. - Compare Negative Cases: check the same factors in cases where the phenomenon never appeared. - Require Both To Agree: accept the causal claim only when positives share the factor and negatives lack it.
Anchor fast decisions
Agreement alone cannot distinguish a cause from a mere correlate, because unrelated factors may co-occur by chance or by shared context. Difference alone struggles when the contrasting case differs in many ways at once. Combining them narrows the candidate set from two directions: the shared factor must be present whenever the effect is present and missing whenever it is not, which removes most accidental correlations.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- zh.wikipedia.orghttps://zh.wikipedia.org/wiki/%E9%80%BB%E8%BE%91%E4%BD%93%E7%B3%BBverified
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