What’s the Difference: Incident and Incidents, Incidence and Incidences

incident_incidence_of_wildfiresAs the United States has struggled with catastrophic hurricanes, wildfires and mass shootings, I’ve heard people stumble over the use and pronunciation of incident and incidents, and of incidence (a valid word) and incidences (not a valid word in plural form).

The following definitions and examples will help you tell the difference.

incident: a noun meaning an event or occurrence; synonyms are episode, happening, escapade, occasion, adventure, proceeding, circumstance, development

These examples show how to use incident and incidents:


The incident occurred at 11:18 p.m.

He has changed since the incident.

The days following the fire passed without incident.


She witnessed a number of frightening incidents last year.

He had several traffic incidents in his youth.

She had five horse-related incidents this riding season.

Now consider incidence, incidental and incidentally.

incidence: a noun meaning the occurrence, rate or frequency of a disease, crime, weather catastrophe or something else undesirable; synonyms are prevalence, amount, degree, extent 

These examples show how incidence differs from incidents:

California has a high incidence of wildfires.

Men have a higher incidence of hair loss than do women.

The incidence of polio has dropped by over 99% since 1988.

Note that incidence is singular in each example; it has no plural form.

These examples define and show how to use incidental and incidentally:

incidental: adjective that means accompanying but not a major part of something; by chance, by accident, fortuitously, by a fluke, by happenstance

I have an expense account for business travel, but I pay incidental costs myself.

Development of the polio vaccine was incidental to Dr. Jonas Salk’s original goal: to develop a flu vaccine.

Citing sources is not incidental to your research paper; sources confirm the validity of your findings.

incidentally: an adverb used when a person has something more to say about or adds a remark not connected to the subject; in an incidental manner, as a chance occurrence

Incidentally, Dr. Jonas Salk, who developed the polio vaccine, neither patented it or nor accepted compensation for its discovery beyond his salary as a researcher.

My sister, incidentally, had a bad reaction to the flu shot she got last week.

Note the pronunciation:

in-ci-DEN-tal-ly (5 syllables), not in-ci-DENT-ly (4 syllables)

I hope this post helps those who struggle with words used to describe an incident; multiple incidents; incidence, the rate of occurrence of incidents; and incidentally, something not relevant to a subject under discussion.

Are there words you hear misused or mispronounced? Let me know in the comments section below or by email.

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Kathy Watson

Kathy Watson has a love/hate relationship with grammar; she loves words and the punctuation that helps them make sense, yet she hates those pesky rules. A self-proclaimed ruthless editor, she prefers standard usage guidelines of The Associated Press Stylebook. Her easy-to-use Grammar for People Who Hate Rules helps people write and speak with authority and confidence. She encourages and welcomes questions and comments. (Email)

2 thoughts on “What’s the Difference: Incident and Incidents, Incidence and Incidences

  1. AvatarRense Houwing

    One remark on the given definition of the concept ‘incidence’ in this comprehensive explanation: since ‘frequency’ means ‘count per time period’ or, in other words, ‘rate of occurrence’ it is incorrect to define ‘incidence’ as ‘rate of frequency’.

    1. Kathy WatsonKathy Watson Post author

      Rense, I agree. When I seek a definition of a word, I often check two or more sources. I vaguely remember my last edit on this and pausing at that wording and punctuation (comma placement). I took time today to revisit one of my sources, and I changed the post to “occurrence, rate or frequency …” consistent with your accurate detection. Thanks for your attention to detail — and for taking the time to comment.

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