Fewer or Less?

When do we use 'fewer than' and when do we use 'less than'?

Both words are comparatives. But they are - usually - used in different situations.

'Fewer' means 'not as many' and refers to things that can be counted and where a plural is possible (eg apples, people):

Fewer than ten apples remained after the meal.

'Less' means 'not as much' and refers to things that are uncountable and do not usually have a plural (eg sugar, time, money);

The organisers had less money and less time than last year.

However, this can be a tricky area when it comes to quantity. For example, with 'ago' we say 'less than' when referring to a single period of time:

I started working here less than six weeks ago. (= one period of time)

For an excellent exercise, see here.

For an interesting discussion about these two little words - 'fewer' and 'less' - see here.