The BBC reports that Tesco is to change its checkout signs to read Up to 10 items, thereby sidestepping the problem of whether it should be 10 items or less or 10 items or fewer. Traditionally I was inclined to mentally amend the former to the latter, but I’ve learned that this ‘correction’ is controvertible.
Generally speaking the difference between fewer and less is like the difference between many and much: one is for stuff you can count, the other is for stuff you can’t or don’t count, e.g. many jobs but much work, fewer jobs but less work. In technical terms, fewer is used with “count nouns“, less with “mass nouns”. So one has fewer banknotes but less money, fewer troubles but less trouble (some nouns have a foot in both count and mass categories). Fewer refers to numbers of things; less refers to measurements or degrees of something.
That’s the general rule, but actual usage is not so simple. Some standard phrases go against the guideline (Write your answer in 100 words or less; He made one less mistake this time), while less is also used with mass nouns when the noun is measured in increments or fractions. Time, distance, money, statistical figures and mathematical amounts can be segmented this way, so one writes:
less than six months
five kilometres or less
less than €100
10 is less than 12½
An exception is when the noun is used in a way that emphasises its distinct units, rather than its fractional nature. One writes “fewer days’ maternity leave” because in this example the days are treated as indivisible blocks.
Merriam-Webster shows how Robert Baker’s mild preference for using fewer with count nouns, which he expressed in 1770, seems to have been subsequently set in stone as an absolute injunction against using less with count nouns. This injunction seems more arbitrary than sound. There are instances when fewer is preferred, but less is often fine when received wisdom says it’s anathema. Less has been used with count nouns for over a thousand years, so it’s about as standard as it gets. The ‘rule’ is a relative upstart.
If in doubt, try them both out – the human ear can be a good guide to usage. If you’re still not sure, there’s a fair chance that either usage is acceptable. Writing less where fewer would be more elegant – or more formal, where so desired – is not going to get you sent you to hell, and if you get sent to Tesco, you’ll be spared the dilemma at the checkout.