* Preposition: This is the most common category for "in." It shows the relationship between a noun or pronoun and another word in the sentence. For example: "The book is in the box." Here, "in" tells us where the book is located.
* Adverb: "In" can also act as an adverb, modifying a verb, adjective, or another adverb. For example: "I am in the house." Here, "in" tells us about the location of the speaker.
* Part of a phrasal verb: "In" can be part of a phrasal verb, like "check in,"" get in,"" fill in." In these cases, the combination of "in" and the verb creates a new meaning.
It's important to consider the context of the sentence to determine the specific grammatical function of "in."