There are only 2 indefinite articles in English: A and An
Use:
For singular count nouns
Use A before consonant sounds
Use An before vowel sounds
Attention: If it is a vowel but it has consonant sound use
A.
Example:
a university (u has the sound [you] as the
consonant y)
If the noun begins with a consonant but the first sound is vowel use An
Example
An hour class (h here doesn’t have any sound, so the first
sound is from O) [anourclas]
Obs.: around 95% of h are aspired like in "a hospital", "a healthy life"
Use only for count nouns. If the word is uncountable you can't use. For example, we do not count milk, we do not say
1 milk, 2 milk
We count only one glass of milk, or one liter of milk, so it is wrong to say
a milk
Then we replace "a" by some: some milk
Comparison with Portuguese:
In
Portuguese there are four indefinite articles: um, uma, uns, and umas.
Use:
They are used according to number and gender:
Um and Uns are used for male nouns
Uma and umas are used for female nouns
Um and uma are used for singular nouns
Uns and umas are used for plural nouns
Example: um
menino (a boy), uma menina (a girl)
Uns meninos
(some boys); umas meninas (some girls)
Notice that in English we can’t use indefinite article for
plural nouns, so we replace by "some" (or any in negative and interrogative
sentences).
