It is common for English speakers to mix up “less” and “fewer”. This is a mistake that even native speakers make fairly often. As a rule, “fewer” is used for nouns that can be counted individually, called count nouns, while “less” is used for things that can’t be counted, or noncount nouns. Compare these sentence sets:
“You should try to eat fewer sugary snacks.”
“You should try to eat less sugar.”
“Fewer distractions in the office would help me work better.”
“Less talking in the office would help me work better.”
These sentences illustrate the difference between count and noncount nouns. Count nouns can be expressed in the plural (like snacks or distractions), while noncount nouns cannot be expressed in the plural (like sugar or talking).
The distinction between “much” and “many” also depends on whether a noun is a count or noncount noun. Much is used for noncount nouns while many is used for count nouns. Putting the 2 rules together, you use “much” and “less” for noncount nouns and “many” and “fewer” for count nouns:
“Eating too many sugary snacks is unhealthy. You should try to eat fewer sugary snacks.”
“Eating too much sugar is unhealthy . You should try to eat less sugar”.
“There are too many distractions in the office. Fewer distractions would help me work better.”
“There is too much talking in the office. Less talking would help me work better.”
The exceptions to less/fewer rule are time, money, and distance. You would say that something costs “less than $100”, not “fewer than $100”, even though dollars can technically be counted. This is because you are referring to the cost as a whole amount. Similarly, you should also say “I’ve lived here for less than six months” or “There’s a supermarket less than 2 blocks away”.
By the way, that sign for the supermarket express lane that reads “10 items or less” is technically incorrect and should read “10 items or fewer” since you can count the individual items. Every so often, a grammarian will point this out but so far it’s been a losing battle.
Hopefully these tips will help you make fewer mistakes with English grammar!