Exceptions to the rule
But, and with language there’s always a but, fewer isn’t used when talking about things that, although plural, are usually considered as a whole rather than a collection of individual items, for example, sums of money. So we would say:
Less than fifty pence; that’s a bargain.
The above ‘but’ comes into play because, when talking about money, we are considering the total amount as a singular item. So, when referring to fifty pence we aren’t usually meaning fifty individual pennies but a total amount of money. So, such items are singular, hence we use ‘less’.
The same goes for distance, time and ages, hence:
It’s less than two miles to the Peak District from here.
Children aged less than four don’t go to school.
Also, fewer isn’t used for numbers on their own:
My weight is under 80 kilos.
Three is less than four.
So, that’s the rules out of the way.
How did the rule come about?
So, why the rule? Let’s step back to 18th century England, at which time, spelling, pronunciation and grammar were highly variable, with some regional dialects being unintelligible to outsiders. In the same way that the advent of railways in 19th century England required the imposition of a standard time, the publishing of books and newspapers in the 18th century induced writers to standardise the language.
Samuel Johnson published his Dictionary of the English Language in 1755. Jonathan Swift, deploring what he called ‘the corruption of the English tongue’, was one of several notables who proposed an academy to arbitrate over what was correct English. This was an attempt to follow Cardinal Richelieu’s Académie Française, which rules on matters pertaining to the French language. The middle years of the 18th century saw a deluge of books on grammar, dictionaries and rule and style guides aimed at expunging ‘barbarisms’ and ‘corruptions’.
At this point, step forward Robert Baker. Not much is known about Baker - he wasn’t a renowned writer or grammarian and he held no especial status in society. And, at this point, I’d like to introduce a portrait of him but there doesn’t appear to be one, which must say something about his status.
In the forward to a 1770 book Baker wrote a plea to King George III:
“My first proposal is that your Majesty would… establish in London an Academy of the Nature of that of the Belles Lettres at Paris… Our language, as has been often observed, is manly and expressive, but our writers abound with Incorrectness and Barbarisms…”
As it turns out, Baker was pleading for a cause that was already largely lost. It had been backed by Queen Anne earlier but, after she died in 1714, support began to peter out. Nonetheless, Baker persisted. In his Reflections on the English Language, 1770, he lists 127 rules, including this, Rule 47:
LESS
This word is most commonly used in speaking of a number; where I should think fewer would do better. No fewer than a hundred appears to me not only more elegant than no less than a hundred, but more strictly proper.
This opinion appears to be the source of all subsequent statements that there is a rule of grammar relating to less/fewer - there are certainly no known prior examples of it in print.
Why do we need a rule?
Well, we don’t. Baker made the rule up for no obvious reason and, also for no clear reason, people accepted it. He claimed no expertise as a grammarian and only expressed it as a subjective preference.
We might wonder why we need such a rule - the substitution of ‘fewer’ for ‘less’ adds nothing to intelligibility.
When considering things that exceed other things we use ‘more’ and this word is considered sufficient for both countable and non-countable things. So, while the rule would have it that we should say ‘fewer cows; less milk’ grammarians are content with ‘more cows; more milk’.
For centuries prior to Baker’s book people had been happy to say ‘less cows; less milk’ and the sky didn’t fall.
The English language needs rules in order for us to understand each other, but for no other reason. Baker’s ‘less versus fewer’ is a rule for rule’s sake and should be sent into the same linguistic oblivion as ‘never split an infinitive’ and ‘never end a sentence with a preposition’. What became of his other 126 rules isn’t clear.
Perhaps prescriptivists might start to lobby for a new ‘extra cows; more milk’ rule, which would after all, be as valid as Baker’s Rule 47.