Listening to someone talk about the incidence of particular types of incidents could leave anyone feeling baffled. We've even had a listener ask us whether people have started using "incidence" as a hybrid of "incident" and "instance."
We don't think so. However, since we're talking about homophones here, it's likely people are just confused.
"Incident" comes into English from French and can be found as far back as the 13th century. It refers to an event or something that happened, often something unusual or unpleasant. You can talk about more than one incident with the plural form "incidents," thus the confusion with "incidence."
"Incidence" also comes into English from French, from the same French word as "incident." It means "frequency." For example, you may have heard someone talking about the high or low incidence of COVID-19 in a particular area, or how the incidence of COVID-19 has risen or declined.
We don't often see its plural form, "incidences," but it shows up once in a while. You could talk about the incidences of COVID-19 in two different populations, for example. Most of the time though, "incidence" appears in the singular.
"I think what has happened here is that these two words have gotten confused,” says English Professor Anne Curzan. “For some people, 'incidence' can refer to something that's happened. For some speakers, 'incidences' is the plural of 'incident.'"
To add to the confusion, we decided to throw "instance” and “instances” into the mix. Listen to the audio above to hear that discussion.