You may have heard the traditional "countable" rule about less versus fewer, but there's also a better rule you may not have heard that covers some of the exceptions to the traditional rule.
If you want a simple rule, the difference between less and fewer is straightforward: The traditional advice is that fewer is for things you count, and less is for things you don’t count.
You can count M&Ms, glasses of water, and potatoes—so you eat fewer M&Ms, serve fewer glasses of water, and buy fewer potatoes for the salad.
You can’t count candy, water, or potato salad—so you eat less candy, observe that the lake has less water, and make less potato salad for the next potluck.
The “Singular Versus Plural” Rule
As I said, that's the simple rule, and the one you'll hear most often, but another way to think about the difference that also takes care of some of the exceptions to the simple rule is to use less for singular nouns and fewer for plural nouns. For example, the Chicago Manual of Style recommends using the “singular or plural” framework.
For the easy nouns, it works the same way:
|Singular: Less||Plural: Fewer|
|Candy is . . . less candy||M&Ms are . . . fewer M&Ms|
|Water is . . . less water||Glasses of water are . . . fewer glasses of water|
|Potato salad is . . . less potato salad||Potatoes are . . . fewer potatoes|
Time, Money, Distance, and Weight
Time, money, distance, and weight are often listed as exceptions to the traditional “can you count it” rule because they take less, but when you use the “singular or plural” rule, time, money, distance, and weight all fall in line. Although a thousand dollars is certainly countable—a bank teller will do it for you gladly—we routinely ignore that fact and think of them as singular amounts:
- He believes $1,000 is a lot of money.
- She says that 50 miles is a long drive for ice cream.
- We think 12 hours is too much time to spend on the road.
They’re singular and they take less:
- We had less than $1,000 in the bank.
- We’re less than 50 miles away.
- I can fix the roof in less than 12 hours.