Genius vs. Ingenious vs. Ingenuous

How to use "genius," "ingenious," and "ingenuous" correctly

This is an entry on my list of Common Errors in English Usage. Visit the main page for direct links to additional entries.

Genius should only be used as a noun, not as an adjective:

genius plan
certifiable genius

Ingenius is an adjective. Someone ingenious is clever, and something ingenious is characterized by cleverness or resourcefulness. The noun form of ingenious is ingenuity.

ingenious architect
ingenious plan

a plan that shows great ingenuity

Someone ingenuous (also an adjective) is innocent, simple, candid, sincere, naive—sometimes to the point of lacking cunning or sophistication. The noun form of ingenuous is ingenuousness, and its antonym is disingenuous.

ingenuous child who couldn’t conceive of lying
seemed ingenuous, but was actually sly

the child’s disarming ingenuousness

a disingenuous explanation that was intended to be misleading

Be sure to spell these words correctly—remember the o in ingenious.

Related Resources

Common Errors in English Usage: Errors in diction and idiom commonly made by native speakers of English

List of Common Errors in English Usage (PDF): Printable version of the complete list

Common Grammar Errors: A list of common errors in grammar (topics like subject-verb agreement and parallelism) as distinct from usage

List of Common Errors in English Usage: PDF version