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.

Often only the direction of causality mentioned here under point 1 (“𝚨 causes 𝐁 ”) is understood as a “real” causal relationship in a strict sense. This makes sense if you consider that otherwise statements such as the following would also describe a valid causal relationship:

The egg fell off the table because it broke.

Obviously, in this context, such a statement is nonsensical. However, whether such a constraint makes sense in other contexts must be decided on a case-by-case basis.

• Causal illusion
• Fallacies of causality
  • Teleological fallacy
• Spurious correlation

• Causality on Wikipedia
• Correlation does not imply causation on Wikipedia