This content is licensed from NYU's American Journalism Online MA Program
There is a similar grammatical logic to ‘less’ and ‘fewer.’ You use ‘fewer’ with things you can count and ‘less’ with things you can’t. Unlike with ‘over’ and ‘more than,’ they are not interchangeable.
He needs to eat fewer M&Ms and more vegetables if he wants to lose weight. (Not less M&Ms, since they are countable.)
She added fewer potatoes to her favorite side dish than usual. (Not less potatoes.)
Fewer than 500 people attended the protest rally. (Not less; 500 people is countable.)
She sank less than 90% of her free throws this past basketball season. (It’s less because 90% is considered a whole unit, although some might disagree.)
I should drink less coffee and eat fewer doughnuts. (Coffee isn’t countable, unless you are counting cups of coffee. Doughnuts are countable.)
Of course, as with ‘over’ and ‘more than’, there can be confusion. If you go to a supermarket, you might see a sign like this by the checkout:
‘Items’ is obviously countable, so you would think it should be “10 Items or Fewer,” except that you could also view these 10 items as one unit. If you do—and most people seem to—then “10 Items or Less” is correct.
And ‘less than’ is used before a plural noun that deals with a measure of distance, amount, time, or weight.
We covered less than 250 miles by sundown.
I have less than $20 in my wallet.
She leaves for Europe in less than two weeks.
He weighs 20 pounds less than he did a year ago.
Like we said, English is full of exceptions to the rules.