Articles are a type of adjective that are used before nouns. Together, an article and a noun form a noun phrase. In English, articles indicate whether the identity of the noun is known to the reader. If so, a definite article is used. Otherwise, an indefinite article is used.

There are 3 indefinite articles in English: a, an, and some. We use indefinite articles when we are not referring to a specific or known entity. We could use these in two situations:

1. We are introducing the noun for the first time. So a story could start as ‘Once upon a time, there was a little girl called Alice who lived with some children in an orphanage.’ We use the indefinite articles for the girl, the children, and the orphanage because this is the first time we are mentioning them.
2. We do not care which one exactly. For example, if you ask your friend to give you a pen or some pens, you don’t care which pen or pens you get. You were not referring to any specific ones.

A’ and ‘an’ are used with singular nouns, e.g. a baby, a glass of juice, and a a tree. In this case, the reader (you) would not know which baby is being referred to. It could be any baby. When the following word starts with a vowel sound, use ‘an’. For example, an apple, an elephant, and an octopus.
2 things to note:

1. You use ‘an’ when the next word begins with a vowel sound, even if the next word is not a noun. For example, “an exciting day”, “an ugly house”, and “an obviously silly situation”.
2. The criteria is that the next word begins with a vowel sound, not a vowel. For example, ‘hour’ begins with a vowel sound because the ‘h’ is silent. So ‘one hour’ is also ‘an hour’. Likewise, ‘university’ begins with a ‘y’ sound, not a vowel sound. Thus we say ‘a university’ not ‘an university’.

‘Some’ is the plural version of ‘a’ and ‘an’. As long as we are referring to a plural indefinite noun, we can use ‘some’. For example ‘some cats’, ‘some boys’, and ‘some white chairs’.

You use ‘some’ with uncountable nouns, ‘some cheese’, ‘some milk’, and ‘some money’.

There is just one definite article in English, “the”. This is used with singular, plural, and uncountable nouns as long as the reader knows which specific thing or things we are referring to. The definite article is therefore used in three cases:

1. We have already introduced it. ‘Once upon a time, there was a little girl. The girl’s name was Alice.’ It is clear to the reader that we are not referring to any girl, but the same little girl that we introduced previously.
2. There is only one such thing that exists or matters. For example, we could say ‘Don’t look directly at the sun.’ or ‘We visited the Statue of Liberty on vacation’.
3. We are describing the exact thing. ‘Do you remember the man who shouted at us yesterday?’

Less commonly, there are also some fixed expressions where you would use ‘the’ even when not referring to a specific item. For example, ‘We went to the beach last week’.

When the following nouns are referred to in a general sense, articles are not used.

1. Abstract nouns (‘Knowledge is power‘, ‘I love technology‘)
2. Uncountable nouns (‘Milk is good for you’, )
3. Plural countable nouns (‘I prefer cats to dogs.’)

However, when referred to in a specific sense, the definite article should still be used.

• Abstract nouns (‘The knowledge of a second language is really useful.’)
• Uncountable nouns (‘Please pass the salt.’)
• Plural countable nouns (‘The cats are making lots of noise.’)

You should also not use articles with:

• names of meals (‘Breakfast was excellent’, ‘I am having lunch‘)
• languages (‘I am learning English‘)
• institutions, unless referring to the building (‘went to prison‘, ‘admitted to hospital‘, ‘accepted into university‘, ‘attended church‘)

Typically, you would also not use articles with proper nouns. Proper nouns are specific names (always capitalized) for a unique thing. These could be persons (Alex, Marta, Mrs. Smith), places (New York, Disneyland, Walmart), or things (Saturn).
However, there are exceptions. If the proper noun is not ‘significant’, you should use articles. For example ‘Let’s eat some Oreos’ and ‘That’s a beautiful Ferrari.’
The definite article ‘the’ is also used with many geographic features (rivers, seas, oceans, gulfs, straits, mountain ranges) and some countries.

Countries

• the United States
• the Virgin Islands
• the Netherlands
• the Czech Republic

Rivers

• the Amazon
• the Danube
• the Nile
• the Thames

Seas and Oceans

• the Baltic (Sea)
• the Black Sea
• the Pacific Ocean
• the Atlantic Ocean

Gulfs and Straits

• the Gulf of Mexico
• the Gulf of Oman
• the Persian Gulf
• the Strait of Gibraltar

Mountains ranges, plateaus, canyons, plains and valleys

• the Himalayas
• the Ural Mountains
• the Tibetan Plateau
• the Grand Canyon
• the Great Plains

Other geographic

• the equator
• the North Pole
• the Sahara (desert)
• the Suez canal
• the Tropic of Cancer