The debate about using fewer or less when referring to quantity still rages. It is related to the concept of descriptive vs prescriptive grammars.
In terms of historical origin, less has been used continuously in English for hundreds of years to refer to comparative quantity with all nouns whilst the use of fewer is fairly recent and applies to countable nouns.
The grammatical difference between the two is fairly straightforward:
less is the comparative for little and is often used with non-countable nouns:
The is only a little sugar left in the bowl.
There is less sugar in this bowl than in that bowl.
fewer is the comparative for few and is used with countable nouns:
There are only a few cars on the road today.
There are fewer cars on the road today than yesterday.
However, in everyday English many people will use less with countable nouns. Phrases like these are common:
? There are less cars on the road today than yesterday.
? We worked less hours than usual.
? a question mark at the beginning of a sentence is used to show a sentence which is grammatically questionable
While Google n-grams finds over 13 million examples of less than it finds just under 600,000 examples of fewer than. This means that regardless of whether you look at countable or non-countable nouns, less is, in fact, far more popularly used than fewer and appears to be driving fewer out of use.
For the TEFL Teacher
As a teacher, should you correct a student who says there are less words to learn or less students in class?
This will depend on whether you are teaching “correct” English as defined by traditional grammars or spoken English as defined by most speakers of English. The question you have to ask yourself is: does it matter? Some people think it does, some people think it doesn’t and who is to say who is right?
n-grams & TEFL– analyzing language for patterns
Descriptive vs Prescriptive Grammars – the difference in how we see language