As a student, you may struggle with countable and uncountable nouns. But fear not because even native speakers have a hard time with it. Or do fear because there is a bloody war in existence that apparently doesn’t want to end.
The rule says that fewer refers to numbers that can be counted (countable nouns) and less to an amount that is measured (uncountable nouns).
|fewer cars||less time|
|fewer choices||less money|
|fewer people||less water|
There are a lot of exceptions to this rule and less is also used with countable nouns. Especially with numbers.
|distance||less than 2 miles|
|time||less than four days|
|money||less than $50|
|figures||less than 100 people|
Less is also very common before regular plural nouns in speech but not in writing, which should be avoided according to Merriam Webster.
The exception is as old as the language itself. However, it seems that two hundred years ago sticking strictly to the rule went into fashion. The trend was huge but less was still widely used. Nowadays, you can find supporters on both sides.
The debate is heated and some even lobby to have things their way. In 2008, one of the most traditional supermarkets in the UK, Tesco, had to change its signs at the quick checkouts. “10 items or less” was too problematic for some complaining customers. Now you should bring “Up to 10 items” if you want to skip long queues at the checkout.
For a good use, just comply with the exceptions for distance, money, time and numbers, both in writing and speaking. Follow the rule for the rest.