We have two main articles in the English language: indefinite and definite.
Indefinite articles
They are: 'a' or 'an'.
If a word starts with a consonant, we use 'a':
👉 She's a teacher.
👉 This is a book.
👉 He's a good singer.
If a word starts with a vowel (a, e, i, o, u), we use 'an':
👉 Give me an apple, please.
👉 She's an actress.
❗️Note that we use 'an' before words where 'h' is silent: an hour, an heir.
❗️Note that sometimes 'u' is pronounced as 'y', that is why we use an article 'a': a university, a unicorn.
When to use indefinite articles
📍 With singular, countable nouns:
✅ I want a sandwich - countable
❌ I'll give you a good advice - uncountable. We say: I'll give you some good / a piece of advice
📍When we talk about something for the first time or name things in general:
👉 This is a cat. The cat is big - in the first sentence we mention 'a cat' for the first time. Then, we continue talking about that cat. It means we already know that cat and that's why we use 'the' in the second sentence.
👉 Do you want an apple? - the speaker speaks about things in general, not about a specific apple.
📍 With jobs:
👉 My brother is a doctor.
👉 She's an engineer.
Definite article
This article is 'the'.
📍 We use it when we talk about specific things. Things that were mentioned before or things that all members of the conversation know about:
👉 This is a cat. The cat is big - in the first sentence we mention 'a cat' for the first time. Then, we continue talking about that cat. It means we already know that cat and that's why we use 'the' in the second sentence.
👉 The cat is sick. We need to visit the vet - we have the only cat in the family.
👉 Look at the girl over there - the speaker's pointing at a certain girl.
📍 With superlative adjectives and ordinal numbers:
👉 This is the biggest dog I've ever seen.
👉 The first car appeared in 1886.
📍 With unique things:
👉 The Sun is shining brightly.
👉The sky is blue.
📍 With musical instruments:
👉 He plays the piano.
👉 She plays the guitar.
📍 With the words cinema, shop, airport, railway station:
👉 Would you like to go to the cinema?
👉 Let's meet at the airport.