Cases Where A/An Cannot Be Used

With plural and uncountable nouns

We do not use the before plural and uncountable nouns to talk about things in general.

With possessives and demonstratives

We do not use the with possessives (my, your) or demonstratives (this, those).

With singular proper nouns.

We do not use the with singular proper nouns.

Between all and a number

The is not normally used between all and a number.