Q: I always thought “fewer” and “less” meant the same thing, but a friend told me I was wrong. What’s the difference?—Anonymous
A: Many people believe “fewer” and “less” are interchangeable, but that’s not true. While both words signify a smaller quantity of something, each has a more specific use.
“Fewer” emphasizes number and modifies plural nouns, as in a smaller number of persons or individual items. Fewer than 20 parents attended last night’s PTA meeting. I have fewer strikeouts than anyone on my softball team.
“Less” focuses on matters of degree, bulk, or quantity. It often modifies collective nouns, mass nouns, and nouns denoting an abstract whole. I asked our former managing editor, Maria Witte, for an example, and she said, “The more you bug me, Brian, the less respect I have for you.” Respect is measured in degrees, so “less” fits.
When examining a sentence, think of it in terms of individual items vs. quantity. I had less than $20 in my wallet (a quantity). I had fewer than 20 one-dollar bills in my wallet (individual items). Once you understand the definitions, you’ll waste less time and have fewer problems with the issue (Hey, that's a good mnemonic device to remember the difference!).
PET PEEVE ALERT: Never, under any circumstances, use “fewer in number” or “fewer number of people.” It’s redundant and unnecessary. “Fewer people” works just fine.