Using 'one' and 'ones' to Replace Nouns

Absolutely. When referring to people, one and ones function identically to how they refer to objects, acting as substitutes for singular or plural count nouns. For example, Which student is the new one? or Among the candidates, the most experienced one was selected. Similarly for plurals: The new employees are adjusting well; the enthusiastic ones pick things up quickly. However, in very informal contexts, he/she or they might be preferred if the specific person is known or easily identifiable.

Not always. If the noun being substituted is perfectly clear from the immediate context, you can omit the adjective. For instance, if someone asks, Do you want a cookie? you could simply reply, Yes, I'll take one. Here, cookie is understood. However, if you are distinguishing between types, an adjective becomes necessary: I'll take a chocolate chip one. Similarly, with definite references: The one on the top shelf is mine. (It's understood to be the item being discussed).

This distinction is crucial for C1 learners. It is a personal pronoun that refers to a specific, unique individual noun instance that has already been fully identified. One is a pro-form that replaces a noun, referring to an item of a certain type or category, or one instance among potentially many similar ones. Think of it as pointing to that exact thing, and one as pointing to any thing of that kind or that particular thing of that kind. If you lose your specific car, It was red. (referring to your car). If you need any car of a certain type, I want a red one. (referring to a type of car). The choice hinges on whether you are referring to a unique object (use it) or a general category/type (use one).

No. One and ones are strictly used for count nouns. Uncountable nouns (e.g., water, music, information, furniture, advice) cannot be replaced by one or ones. If you need to refer to a quantity of an uncountable noun, you might use phrases like some, a lot, or rephrase the sentence entirely. For example, instead of I need some sugar. Do you have a brown one? (incorrect), you would say, I need some sugar. Do you have any brown sugar? or Do you have some of the brown variety?

Yes, absolutely. One and ones are standard grammatical constructs and are entirely appropriate for formal writing. Their use enhances clarity and conciseness, which are valued qualities in academic and professional prose. The key is to use them precisely, ensuring the antecedent is clear and the choice between one and it is grammatically sound. Misuse, rather than the use itself, would be deemed informal or incorrect.

These are two distinct grammatical functions of the word one. As a noun substitute, one replaces a specific or generic count noun (I need a pen. I'll take this one). As an indefinite pronoun, one refers to a generic person or people in general, similar to you in an impersonal sense, primarily in formal contexts. For example, One should always be polite. or If one wants to succeed, one must work hard. The context will always clarify which function one is performing.