Questions & Answers about Я покупаю эти чёрные брюки.
Why do we use эти instead of этот or это?
эти is the plural form of the demonstrative pronoun (meaning "these"). We use it here because it has to match the plural noun брюки (trousers).
How is the plural adjective чёрные formed?
The dictionary form is чёрный (black). To make it plural to match брюки, we change the ending to -ые. Most plural adjectives in the nominative case end in either -ые or -ие.
Shouldn't "these black trousers" be in the accusative case since they are being bought?
Yes, they are in the accusative case! However, for plural inanimate objects (things that aren't alive, like clothes), the accusative case endings look exactly the same as the nominative case. That is why we use the nominative plural forms эти and чёрные.
Does брюки have a singular form if I only buy one pair?
No, just like in English (where we say "pants" or "trousers"), брюки is a plural-only noun. Even if you are buying just one pair, you must always use plural pronouns like эти and plural adjectives like чёрные with it.