Cause and Effect

The five standard relationships

• I caused II: event I happened first and produced event II.
• II caused I: event II is the cause; event I is the effect.
• Both effects of a common cause: a third unstated event produced both.
• Independent causes: the events are unrelated.
• Effects of independent causes: each event has its own separate cause; the two events do not influence each other.

The temporal-order test

Causation requires the cause to come before the effect. If event II clearly happened first, then I cannot have caused II. Read the time markers in the statement ("last week", "yesterday", "immediately afterward") before judging direction.

Worked example

Event I: The government raised petrol prices. Event II: Public-transport fares increased.

Petrol is an input cost for transport, so a rise in petrol prices typically causes a rise in transport fares. Direction: I caused II.

Worked example with common cause

Event I: Many farmers in the province committed suicide last year. Event II: Crop yields fell sharply across the same province.

A drought, flood, or pest attack could plausibly cause both farmer distress and reduced yields. Neither event directly causes the other; both are likely effects of a common cause. Answer: both are effects of a common cause.

The independence test

If you cannot construct any plausible causal link in either direction, and no shared third cause is plausible, the events are independent. This is the rarest answer; default to it only when every other explanation fails.

Common traps

• Reverse causation: students assume A caused B without checking whether B might have caused A.
• Correlation without cause: two events occur together but neither causes the other (e.g. ice-cream sales and drowning both rise in summer; the common cause is hot weather).
• Time gap: if the events are months apart, a direct causal link is less plausible.