The distinction between “less” and “fewer” lies at the heart of clear and accurate English usage. Using the right words makes your communication clear and sharp, in both writing and speaking.
Definition of Less
“Less” is used with uncountable nouns, which refer to substances, qualities, or concepts that cannot be counted individually. Uncountable nouns are often singular and represent a mass or a quantity rather than discrete units.
Explanation of Use with Uncountable Nouns:
“Less” modifies nouns as a whole or a collective mass. These nouns are not plural and cannot be separated into individual items. Common examples of uncountable nouns include “water,” “money,” “time,” “sand,” and “information.” When we want to indicate a smaller quantity of such nouns, we use “less.”
Examples:

“There is less water in the bottle.”

“She has less money than she did last month.”

“We need less time to complete this project.”
In each example, the noun (“water,” “money,” “time”) is uncountable, and “less” correctly indicates a smaller quantity of the whole.
Definition of Fewer
“Fewer” is used with countable nouns, which refer to individual items that can be counted separately. We can use numbers to tell how many of something there is, because these nouns refer to things that can be individually counted. They also have both a singular and plural form.
Explanation of Use with Countable Nouns:
“Fewer” modifies nouns that represent distinct, countable entities. These nouns can be counted as individual units, making “fewer” the appropriate choice when referring to a smaller number of such items.
Examples:

“There are fewer apples in the basket.”

“She received fewer emails than yesterday.”

“We need fewer chairs for the meeting.”
In each example, the noun (“apples,” “emails,” “chairs”) is countable, and “fewer” correctly indicates a smaller number of individual items.
Examples
To further illustrate the correct usage of “less” and “fewer,” consider the following pairs of sentences:

Correct: “There is less milk in the fridge.”
Incorrect: “There are fewer milk in the fridge.”
Here, “milk” is uncountable, so “less” is used correctly.

Correct: “There are fewer students in the class.”
Incorrect: “There is less students in the class.”
Here, “students” are countable, so “fewer” is used correctly.
Another common context where the distinction is often blurred is in supermarkets and public signs:

Correct: “10 items or fewer” (referring to countable items)
Incorrect: “10 items or less.”
Understanding these fundamental differences and practicing their correct usage can help avoid common mistakes and enhance overall communication clarity. By recognizing whether a noun is countable or uncountable, you can easily determine whether to use “less” or “fewer,” ensuring precise and effective expression.