3.2 Determiners
Determiners are small words you put in front of a noun which tell you something about the thing (person, idea, etc.), but not as much as an adjective would. Determiners include a/an, the; this, that, these, those; my, your, his, her, our and their. You could put any of the determiners in the list in front of a noun like car, house or family, and it would tell you something about it, but it wouldn’t give you a clearer idea of what the thing was like:
her car, their house, his family (determiner only)
her noisy car, their tiny house, his appalling family (determiner plus adjective)
We use a or an – known as the indefinite articles – when we’re referring to something for the first time:
I saw a squirrel outside the kitchen window this morning eating an orange.
You use an when the next word starts with a vowel, as in orange. Notice that the (the definite article) is used before things that you know about already (such as the kitchen window). You would also use the if you were to refer to the squirrel (or the orange) again, as you’ve already introduced these things into conversation.
Determiners can also help you to identify which one(s) of a range of things you mean (this restaurant, that mountain, those shoes) and they can tell you who something belongs to (my idea, our picnic, your nonsense).