A pretty simple one today: this is something that many people are curious about. Both are clearly similar, but what’s the difference between them?
The basis of the distinction between them is whether they’re used with countable or uncountable nouns. I’ve touched on the difference between these two types before, and they’re easy enough to figure out anyway (can I count this or not?), but here’s a quick primer. A countable noun can be made plural, and you can put a number or the articles a or an before them. For example:
Uncountable nouns, also known as mass nouns, can’t be pluralised, and you can only use the before them. Some of the most common are: money, time, water, and basically any feeling or abstract concept like happiness.
Of course it’s not always going to be that simple, and occasionally a word can be either countable or uncountable, depending on the context. Think about pizza or cake, for example. You might buy a large pizza (countable), but you can’t eat all of it, so you just have some pizza (uncountable). When talking about hair, it’s usually uncountable, but if you’re referring to individual hairs, it becomes countable, e.g. Marge Simpson has blue hair, and Homer has three black hairs on his head.
By now, you’ve probably already figured out when to use less and fewer. Less is used with uncountable nouns, and fewer with countable nouns. For example:
Fewer people (countable) are buying houses these days, because they have less money (uncountable).
And that’s it really. There are no annoying exceptions in this case. Perhaps you’ve already known this and have always used them correctly. Perhaps though, you’ve been confused, or, as is the most common issue people have with these words, you’ve been using less with both countable and uncountable nouns.
I’m not sure why this is such a common error. My instinct is that fewer sounds more formal, but I’m not exactly sure why that is. And less is shorter, which probably helps its case. More importantly though, we never really need to distinguish between countable and uncountable nouns. It’s something we know instinctively. We therefore don’t stop to think about whether to use less or fewer. Plus, it doesn’t really cause confusion if you use the wrong word. If you use less before a countable or uncountable noun, the meaning is still clear, so most of us just use less. Of course there are situations when it’s to your advantage to be grammatically correct, and it’s often good to know the right word to use just for your own sake. But at the same time, if you’ve been using only less all this time, don’t panic, as few people will have noticed!
This also applies, by the way, to the words number and amount. The former should strictly be used with countable nouns, and the latter with uncountable nouns. For example:
The number of people buying houses has decreased, because fewer people have the necessary amount of money.
But again, if you’ve only been using amount, don’t panic: the number of people who care about such grammatical strictness is low!