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.

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

1. 𝚨 causes 𝐁 (direct causal relationship).
    
2. 𝐁 causes 𝚨 (reverse causal relationship).
    
3. A third event 𝐂 causes both 𝚨 and 𝐁 (external causal relationship).
    
4. 𝚨 causes other events: e.g. 𝐂, 𝐃, etc, which in turn cause 𝐁 (indirect causal relationship).
    
5. 𝚨 and 𝐁 are not causally connected, but only occur together by chance (spurious correlation).
    
6. 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. frequency illusion, 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.

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 physics) or less strict (e.g. in the social sciences), but they usually contain at least the following minimum requirements:

1. A high correlation of the properties.
    
2. A plausible mechanism of effect.
    
3. A comprehensible chronological sequence of events.

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

• Spurious correlation
• Causal illusion

• Causality on Wikipedia