If you've been to the grocery store lately, you've probably noticed a sign at checkout that says "15 items or less." You'll learn in this lesson that the sign should say "15 items or fewer." The reason is straightforward—when talking about a quantity you can count with numbers, use fewer, but for an amount you can't count, use less. Below are some examples:
There are fewer students here today than there were yesterday.
Use fewer because you can count the number of students. Maybe there were 30 students in class yesterday and only 25 today.
The teacher assigned less homework today than he did yesterday.
Use less because the word homework is not countable. It's not possible to make homework plural—homeworks is not a word. You wouldn't say I have three homeworks tonight ... and that actually leads us into this lesson's hint:
You gave him less pie than you gave me.
Yes, it's true that you can add s to the word pie to make it plural. However, this sentence is talking about the amount of pie, not how many pies, so use less.
Last year's pie-eating contest champion ate fewer pies this year than last.
This sentence tells us that there is more than one pie. Maybe last year he ate 10 pies, but this year he could only choke down 8. Because you can count the number of pies, use fewer.
Be careful when discussing time, measurements, or money. These often seem countable, but in reality they refer to an amount, so use less, not fewer.
Our business pulled in less than $100,000 last year.
You'll be able to finish the race in less than 10 minutes.