incidence vs. incidents vs. instances  

What is the difference between incidence, incident, and instance?

The word incidence is what’s known as an uncountable noun, which means it cannot be divided or counted as individual elements or separate parts. (Subsequently, this means that uncountable nouns are usually not made into plurals, so we would normally not write incidences.) Most commonly, incidence means “the rate, degree, or extent of occurrence or effect,” as in:
  • “There has been a higher incidence of car thefts in the last few months than in the previous five years.”
Where things get confusing is with the words incident and instance, both of which can mean “a particular occurrence.” More specifically, writers have trouble with their plural forms: incidents, which has the exact same pronunciation as the singular incidence (/ˈɪnsɪdəns/), and instances (/ˈɪnstənsəz/), the ending of which sounds the same as the uncommon plural incidences. Because of these shared pronunciations, as well as the relative proximity in meaning, it’s a common mistake to use the plural incidences in cases in which incidents or instances would be the correct term. For example:
Another possible mistake is to use incidents when incidence is the correct term, as in:

*incident vs. instance

Be careful with these two words as well, because they are not always synonymous. While they both can mean “a certain case or occurrence,” incident has another meaning of “a disruptive or violent occurrence that interrupts normal proceedings”; instance cannot be used this way. For example:
Instance, meanwhile, can be used to mean “an example cited to demonstrate or prove something,” which is not how incident is used. For example:

Spelling Tricks and Tips

One way to remember which spelling is correct is to look at the other words used in the sentence. While it is possible to pluralize incidence as incidences, this is not common and, as a result, we almost always find incidence accompanied by singular verbs (such as has in the first example). If we are using a verb that agrees with third-person subjects (such as have or are), then incidents or instances are much more likely to be correct.

1. Choose the sentence in which incidence is the correct spelling.

2. Choose the sentence in which only incident is the correct spelling.

3. Choose the sentence in which only instance is the correct spelling.

4. Choose the sentence in which either incident or instance is correct.

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