I often hear people say "less than", but shouldn't it be "lesser than"? Which one is correct?
Less, lesser, and littler are all comparative forms of little. They are used like this:
little - littler - littlest when you mean "small in size"
little - less - least when you mean "small in amount"
little - lesser - least when you mean "inferior or smaller in importance"
So if you mean one quantity or number is smaller than another, you say "less than".
You would say less than or the lesser of. Not lesser than.
However, it largely depends on the sentence in which you're using your particular example, as it may be that using 'fewer than' instead of 'less than' is correct.
- 'Less' means not as much
- 'Fewer' means 'not as many'
For example, if I'm holding three apples I have 'fewer than 4 apples'.
If I'm holding half a kilogram of sugar, I have 'less than a kilogram of sugar'.
Here's a BBC article highlighting this often-made mistake: http://news.bbc.co.uk/1/hi/magazine/7591905.stm