Why is it so easy to confuse less and fewer? Perhaps because they both represent the opposite of the comparative adjective more. Luckily, the conundrum of less vs. fewer has a solution that is simple to remember. It involves deducing whether fewer or less will be working with a countable or uncountable noun in your intended sentence.
In English, we use the same word, more, for a greater number and a greater amount/quantity. There is little doubt about when to use more.
Could you give Cookie Monster more milk to wash those down with?
Cookies is a countable noun; it is possible to count cookies. Milk, on the other hand, is an uncountable noun; it is a liquid that we measure in terms of volume. Uncountable nouns are always singular.
That quick check confirms that milk is an uncountable noun.
The Difference between “Less” and “Fewer”
Fewer means “not as many.” We use fewer with countable nouns like cookies.
Less means “not as much.” We use less with uncountable nouns like milk.
Most often, you will not have to be Sherlock Holmes to deduce whether a noun is countable or uncountable, thus the decision between less and fewer will be an effortless one.
Molly has been drinking less water than she should on this dry day.
David makes fewer grammatical mistakes than the average person.
My new furniture leaves me with less space for yoga practice.
As the days passed, the rose had fewer petals left on it.
In these examples, determining the countability of the nouns involved was easy. People, grammatical mistakes, and petals are all countable nouns. As difficult as it would be to count all the people who use plastic water bottles, it would be possible to enumerate them because they are itemizable individuals.
Plastic, water, and space, on the other hand, are uncountable; we only describe them in quantities. To make them countable, we would be obliged to compartmentalize them in some way (e.g., pieces of plastic or glasses of water). Nouns that can be further defined and measured in this way make the distinction trickier. For example, here are two sentences with almost the same meaning, but one requires fewer while the other requires less.
Now that my commute is shorter, I use less gasoline each week.
In the first sentence, fewer is used with the countable compound noun gallons of gasoline. In the second, less is used with the uncountable noun gasoline.
“Less vs. Fewer” with Money
Although we can count money, it is usual for us to think of money as a bulk quantity rather than an aggregate of currency units. Therefore, we use less rather than fewer.
It would not be wrong to say, “Rebecca has fewer than twenty dollars left,” but it would seem awkward and unexpected to your reader.
“Less vs. Fewer” with Time
It is also customary to use less with regard to time, even though we can count time in seconds, minutes, hours, and so on.
I wish I could spend less time on household chores.
Yet, depending on how general or specific your reference to time is, it may require the use of fewer.
“Less vs. Fewer” with Weight
Weights are also nouns that are measured in a countable way, yet are customarily used with less rather than fewer.
Even though the pandas’ weight is countable (and in fact we did count it, in grams), it would seem awkward to write, “Baby pandas weigh fewer than 200 grams at birth.”
“Less vs. Fewer” and Percentages
Determining whether percentages represent something countable or uncountable can be tricky. To decide whether to use fewer or less with a percentage, you will have to look at the bigger picture and ask yourself, “What is this a percentage of? Is it countable?”
Although counting the world’s people would be an unenviable task, it is possible to count individual people. Therefore, eight percent of the world’s people is countable and we use the word fewer.
As determined as the speaker in this sentence might be, it would not be possible for him or her to enumerate the uneaten percentage of potatoes. Therefore, we use the word less.