This is another of those conundrums we all face when we are working with words. Do I say ‘fewer vases’ or ‘less vases’? The answer is simple: if you can count the items you are talking about, you use ‘fewer’ and if you can’t count them, you use ‘less’.
So, some examples:
I have fewer / less stationery now than I had at the start of the year.
Can you count ‘stationery’? Try it: One stationery, two stationery, three … Sounds a bit silly, doesn’t it? So, the correct way to say this is:
I have LESS stationery now than I had at the start of the year.
But you can count pens, can’t you? So let’s try the same sentence, substituting ‘pens’ for ‘stationery’.
I have fewer / less pens now than I had at the start of the year.
The same question applies: can you count pens? One pen, two pens, three pens. Yep, pens are ‘countable’ nouns, so you can use ‘fewer’.
I have FEWER pens now than I had at the start of the year.
One way to tell if you use fewer or less is to decide if the noun you are describing is singular (there is just one item or category of items being discussed) or plural (you’re talking about multiple units of the item). If it’s singular, you use ‘less’ and if it’s plural, you use ‘fewer’.
Another way to work out which word to use, is to remember that those aisles at the supermarket which have ’15 items or less’ are GRAMMATICALLY INCORRECT. Of course, we use ‘less’ in this context, as we’re all used to this expression. We’d never change these signs; they’d look odd with ’15 items of fewer’, wouldn’t they? But they are grammatically incorrect. So, if you can remember that, you can remember which word to use in other examples.
Of course, English being the complex language that it is, there are exceptions to this rule when the quantity mentioned is considered a single entity. This is why we can say ‘Entries must be 50 words or less’ and ‘Stopping distance must be 10 metres or less’.
When in doubt, rewrite the sentence so that the problem disappears. ‘I don’t have as many pens now as I had at the start of the year’ completely removes the problem. And will probably result in fewer headaches for all concerned.