Use a / an when the listener doesn't know which one you mean, or it doesn't matter: I talked to a manager. Use the when you both know exactly which one: I talked to the manager. (the one we both know about)
Same situation, two choices. Pick an example.
I talked to a manager.
One of several, and the listener can't tell which. It's new information, or it doesn't matter.
I talked to the manager.
One is in the spotlight: mentioned before, clear from the situation, or the only one.
| Rule | A / An | The |
|---|---|---|
| Nouns | Singular countable only: a book | Any noun: the book, the books, the water |
| Does the listener know which one? | No, or it doesn't matter | Yes |
| Typical uses | First mention, jobs, one of many | Second mention, only one exists, superlatives |
| Example | Can I borrow a pen? | Can I borrow the pen on your desk? |
I bought a shirt and a jacket. _____ jacket was on sale.
Paste an email or an essay. Clarigram marks the mistakes you actually make, shows the rule behind each one as a picture, and builds your practice from them.
Yes, if the listener can still tell which one you mean: Close the door (the one in this room), The sun is hot (there's only one), The man who called you is here (the rest of the sentence tells you which).
Saying someone's job puts them in a group: She's an engineer means she's one of all the engineers. English needs a or an here, even though many languages use no article.