Morality is about right and wrong: "The debate turned on the morality of the decision." Mortality is about death — either the fact of being able to die or the rate at which people do: "Infant mortality has fallen sharply." A single t separates two entirely unrelated ideas.
The core difference
Morality belongs to ethics. It covers the principles by which people judge conduct good or bad, and the conduct itself. Mortality belongs to death. It names the condition of being subject to death, and in statistics it names the number of deaths in a population.
The extra t in mortality is the whole visual difference, which is why the pair survives spellcheck untouched and turns up in published work.
Using morality
- He questioned the morality of accepting the sponsorship.
- Public morality has shifted considerably in thirty years.
Related words: moral (adjective and noun), morals (personal principles), moralise, immoral, amoral. Note the difference between immoral, which means violating moral standards, and amoral, which means operating outside them altogether.
Using mortality
- Mortality among untreated patients was close to forty per cent.
- A bad fall in his sixties made him aware of his own mortality.
Related words: mortal, immortal, mortally, and in statistics the compound mortality rate. Mortality is also the standard term in epidemiology and insurance, where it always means death rates.
The test
Mortality has two senses, so try both. Substitute death rate: if the sentence still makes sense, you want mortality — "infant death rate" works. If that fails, substitute being subject to death: "aware of his own being subject to death" is clumsy but it holds the meaning, so mortality is still correct. Only if neither death sense fits should you reach for ethics — and if "the ethics of the decision" works, you want morality.
The root that fixes it
Mortality carries the Latin element mort-, meaning death, which you already know from mortuary, mortgage's grimmer etymology aside, mortal and post-mortem. If you can see mort at the front, the word is about death. Morality has no such element — it comes from the Latin for custom or manners, the same root behind mores.
Where the error shows up
Medical and news writing is where it bites: "morality rates" instead of mortality rates is a recurring headline blunder, and it inverts the meaning of the sentence completely. The reverse error — "mortality tale" for morality tale — is rarer but funnier.
Also worth keeping straight is the phrase morality play, a medieval dramatic form in which abstract virtues and vices appear as characters. The term is now used loosely for any story with a heavy-handed ethical lesson, and it never takes the t.
Frequently Asked Questions
Is it "mortality rate" or "morality rate"?
Mortality rate — the number of deaths in a population over a given period. "Morality rate" is not a term at all.
What does "confronting your own mortality" mean?
Coming to terms with the fact that you will die. It usually describes a moment such as illness, an accident or a bereavement that makes the fact feel real.
What is a morality play?
A medieval drama in which virtues and vices appear as characters to teach a lesson. The phrase is now used loosely for any story with an obvious moral, and always uses morality.