The words but, while, and whereas can be confusing for students. They seem like they serve the same function, which is to compare and contrast things. However, there are differences that mean these words are not interchangeable.
In English, we use the word but when we are comparing or contrasting features of the same thing. It is coordinating conjunction and it links two independent clauses in a compound sentence.
The dog is tired but happy = the dog is tired but the dog is happy
(We don’t repeat “the dog.”)
The sea is wild but beautiful = the sea is wild but the sea is beautiful
(Again, remember that we don’t need to repeat “the sea.” We just keep it in our mind.)
In these examples, we cannot simply use whereas in place of but:
The dog is tired whereas happy.
The sea is wild whereas beautiful.
When we use but we are introducing something opposite the original idea. If you friend says, “I like going to the cinema, but…” then you know she will say something negative. For example, “I like going to the cinema, but it’s a bit expensive.”
Here are some more examples:
The wine is delicious but cheap.
The book was long but engaging.
Yesterday was cold but sunny.
Remember that in each case we are comparing the first item (the noun) in terms of both following items (the adjectives) but we don’t need to repeat the noun.
Unlike but, we use whereas to compare and contrast the features of different things. (Also not that this is a subordinating conjunction.)
Tigers have stripy fur whereas leopards have spots.
They say that fashion is temporary whereas style lasts forever.
In Southern France the winters are quite mild whereas in the north they can be cold.
In all three examples, we are comparing the features of different things: tigers and leopards; fashion and style; Southern France and Northern France.
We can also use while to compare and contrast ideas. However, unlike the previous two words, we typically use while at the beginning of a sentence. This marks a dependent clause, making these sentences complex.
While she didn’t study very heard, she still got good grades in her exams.
While he may be rich, he certainly isn’t handsome.
While the food in that restaurant is top quality, the service is atrocious.
In each example, we are introducing an idea that contrasts with the idea in the second clause. For example, it is surprising that she got good grades because she didn’t study!
We can’t reverse the sentence order:
He certainly isn’t handsome while he may be rich.