Q. Hi. My fellow editor and I disagree about the use of “less” and “fewer” when talking about percentages. In the example he asked me about, the first phrase of the sentence said something about a certain number of women who do something, then the following phrase said something like “less than 5%” did something else. My fellow editor says that because the sentence is referring to (multiple) women, the phrase should say “fewer than 5%,” while I believe that because the sentence is talking about a percentage (a single quantity), it should say “less than 5%.” None of our sources is helpful with this question of whether a percentage is a single quantity or a number. Please help straighten us out . . .
A. Let’s start with the usage note in The American Heritage Dictionary (5th ed., 2022), under “less”:
The traditional rule holds that fewer should be used for things that can be counted (fewer than four players), while less should be used with mass nouns for things of measurable extent (less paper; less than a gallon of paint). . . . Less [however] falls in the same class as some and more and is used in some well-established constructions where fewer would occur if the traditional rule were applied. Less than can be used before a plural noun that denotes a measure of time, amount, or distance: less than three weeks; less than $400; less than 50 miles. Less is sometimes used with plural nouns in the expressions no less than (as in No less than 30 of his colleagues signed the letter) and or less (as in Give your reasons in 25 words or less). And the approximator more or less is normally used after plural nouns as well as mass nouns: I have two dozen apples, more or less. To use fewer in such constructions sounds fastidious, so writers who follow the traditional rule should do so with caution.
The phrase “less than 5 percent” could be added to the examples above with plural nouns denoting a measure of time, amount, or distance. If so, “less than” would refer primarily to the amount “5 percent,” which only in turn refers to the number of women (see also CMOS 9.20).
Fowler’s (4th ed., Oxford, 2015) points out that “less” has not always been considered incorrect with countable things (the usage began to face condemnation in the eighteenth century). It’s a matter of the right idiom and not really a matter of meaning. If you were to say, for example, “less than five cats,” no one would misunderstand you.