Cause, manner and mechanism of death are three different questions
Death certificates in Britain and the United States separate three things. The cause is the disease or injury, such as cancer. The mechanism is the final physiological failure, such as an irregular heartbeat. The manner is a legal judgement, natural, accidental, homicide and so on, and it can hinge entirely on context.
Coroners, medical examiners or police usually decide the manner, and it is filed as a vital statistic. Categories range from broad labels like 'natural' to narrow ones like 'traffic accident', and there is no international standard for sorting natural from unnatural deaths. International Classification of Disease codes are sometimes used so that statistics can be compared across jurisdictions. An autopsy may be ordered when the law requires it, when the medical cause is unclear, when relatives ask, or when circumstances look suspicious.
The three layers can point in startlingly different directions. One textbook-style example: a person's brain is starved of blood, the mechanism; the underlying cause is a tumour; but if that tumour was induced by radiation deliberately given to harm them, the manner is recorded as homicide. Even 'natural' is slippery. Pneumonia killing a frail 80-year-old is likely to be called natural, while the same infection suddenly killing a healthy 25-year-old usually is not. Heart deaths triggered by trauma are especially ambiguous, and a 1969 California case, People v. Stamp, showed liability can attach even to a death ruled natural.
Old age once served as a catch-all label because doctors could not identify what had actually failed. Modern medicine can usually find the true cause, though the phrase survives partly as a comfort to families. When evidence runs out, as with a partial skeleton, the manner may be left undetermined. Jurisdictions disagree about deaths without a body, such as people lost at sea: some file them as undetermined, others under 'other'. Norway's medical association goes further, treating sudden unexplained deaths and deaths in detention as unnatural.
In England and Wales most deaths are certified by a doctor without any coroner involvement. When a coroner, an independent judicial officer, does step in, an autopsy is almost always performed, but a formal inquest usually is not, and coroners may give descriptive 'narrative verdicts'. The label has practical consequences: homicide rulings go to police or prosecutors, and some life insurance policies treat suicide as grounds to refuse a claim.
Source: Manner of death
