====== Causality ======

Describes a //cause-effect// relationship between two events or phenomena, i.e. that one is caused by the other.

> A short circuit in an electrical appliance caused the house fire.

It is important to distinguish the concept of causality from that of //correlation//, which refers to the co-occurrence of events or phenomena but does //not// imply a causal relationship.

===== Description =====

<aside info>
**Note:** The term "causality" describes a complex concept that has been the subject of controversy in philosophy and science, litterally for millennia. It would go far beyond the scope and possibilities of this site to present the topic or the controversies in a way that is fair to their complexities. The following can therefore not be more than a first approach to the subject.
</aside>

As a general rule, when phenomena 𝚨 and 𝐁 occur in correlation (i.e. either simultaneously or consecutively), the following possibilities must be considered:

  - 𝚨 causes 𝐁 (//direct// causal relationship). \\  
  - 𝐁 causes 𝚨 (//reverse// causal relationship). \\  
  - A third event 𝐂 causes both 𝚨 and 𝐁 (//external// causal relationship). \\  
  - 𝚨 causes other events: e.g. 𝐂, 𝐃, etc, which in turn cause 𝐁 (//indirect// causal relationship). \\  
  - 𝚨 and 𝐁 are //not// causally connected, but only occur together by chance (<span maniculus "see:"></span>[[:mathematics:statistics:misinterpretations:spurious correlation|spurious correlation]]). \\  
  - 𝚨 and/or 𝐁 are observational errors and at least one of the phenomena does not occur at all in the form described (e.g. <span maniculus "see:"></span>[[:psychology:kognitive_biases:frequency_illusion|frequency illusion]], <span maniculus "see:"></span>[[:mathematics:statistics:misinterpretations:base-rate fallacy|base-rate fallacy]], etc.)

The fact that 𝚨 and 𝐁 //correlate// with each other, i.e. that they regularly occur together, is not sufficient to postulate a causal relationship.

<aside important>
<strong>Remember:</strong> Correlation does <em>not</em> imply causality!
</aside>

However, the question of //when// a causal relationship actually exists is rather difficult to answer. Ultimately, different scientific fields have come up with various different – in some cases even contradictory – definitions of causality. These may be more (e.g. in [[wp>Physics|physics]]) or less strict (e.g. in the [[wp>Social science|social sciences]]), but they usually contain at least the following minimum requirements:

  - A **high correlation** of the properties. \\  
  - A **plausible mechanism** of effect. \\  
  - A comprehensible **chronological sequence** of events.

It should however be noted that for each of these criteria there are also problem cases and exceptions.

===== See also =====

  * [[:mathematics:statistics:misinterpretations:spurious correlation|Spurious correlation]]
  * [[:psychology:kognitive_biases:causal_illusion|Causal illusion]]

===== More information =====

  * [[wp>Causality]] on //Wikipedia//

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