1. Countable nouns: singular vs. plural

Countable nouns are things we can count: 1 book, 2 books; 1 chair, 5 chairs; 1 friend, many friends.

• Singular countable nouns (one thing) must have a determiner, like a/an, the, this, my, etc.
• Plural countable nouns (two or more things) can be used:
  • with nothing (zero article), when we speak in general;
  • or with words like some, many, a few, etc.

Singular: needs a determiner

• ✅ I have a book.
• ✅ I have this book.
• ❌ I have book. (incorrect)

Plural: with or without a determiner

• ✅ I like books. (books in general)
• ✅ I bought some books. (an indefinite number of books)

2. a vs. an: basic form

We use a before a consonant sound and an before a vowel sound.

• a book, a car, a teacher
• an apple, an hour, an engineer

Notice: it depends on the sound, not only the letter. For example, an hour (/ˈaʊər/) starts with a vowel sound.

3. Using a/an with singular countable nouns

3.1 Talking about one thing (not specific)

Use a/an when you talk about one thing for the first time, or when it is not important which one.

• I’m looking for a pen. (any pen, not a specific one)
• She lives in an apartment near here.

3.2 Talking about someone’s job

Use a/an after be to talk about jobs and professions.

• My sister is a doctor. (Mi hermana es médica.)
• He’s an engineer. (Él es ingeniero.)
• They are teachers. (plural → no a/an)

3.3 Talking about “what kind of person” or “what kind of thing”

Use a/an to describe the type of person or thing, often with a noun like optimist, person, city, book, story, etc.

• She is an optimist. (She usually feels positive.)
• New York is a big city.
• That was a good idea.

4. a/an in common expressions (appearance)

4.1 Parts of the body (singular)

We use a with singular countable nouns like nose, face, mouth, chin to describe appearance.

• He has a long nose. (Tiene la nariz larga.)
• She has a round face. (Tiene la cara redonda.)

4.2 Parts of the body (plural)

With plural body parts (like eyes, ears, teeth), we don’t use a/an. We can use adjective + plural noun.

• She has blue eyes. (Tiene los ojos azules.)
• He has big ears. (Tiene las orejas grandes.)

5. Using some with plural countable nouns

Important: We do not use some with singular countable nouns.

5.1 Meaning 1: an indefinite number (we don’t say how many)

Use some with plural countable nouns when the exact number is not important or not known.

• I bought some books. (I don’t say how many.)
• She has some new clothes. (Tiene ropa nueva.)
• I met some friends of mine at the party. (Me encontré con unos amigos míos en la fiesta.)

5.2 Meaning 2: “some but not all”

Use some to say that part of a group, but not all of the group, has a certain characteristic.

• Some children learn fast. (But not all children.)
• Some people love spicy food. (But not everyone.)
• Some students arrived late. (Not all of them.)

6. Do NOT use some when speaking in general

When we talk about things in general (all in general, not a part), we usually use the plural with no article (zero article), not some.

• ✅ Children learn languages quickly. (children in general)
• ❌ Some children learn languages quickly. (This means “some but not all children”, not “children in general”.)

• ✅ Cats are independent animals. (cats in general)
• ❌ Some cats are independent animals. (means: some, but not all cats)

More examples:

• Teachers work hard. (teachers in general)
• Smartphones are expensive. (smartphones in general)

7. Quick summary

• Singular countable → must have a determiner: a/an, the, this, my, etc.
• Plural countable → can be:
  • without a determiner: children, books, cats (general meaning), or
  • with some: some children, some books (an indefinite number, or some but not all).
• Use a/an:
  • for one, nonspecific thing: a book, an idea;
  • for jobs: a doctor, an engineer;
  • for types of people/things: an optimist, a big city;
  • in descriptions like a long nose, but blue eyes.
• Use some with plural countable nouns:
  • for an indefinite number: some new clothes;
  • for “some but not all”: some children learn fast.
• Don’t use some for general statements. Use the bare plural: Children learn fast.