What type of phrase or clause provides essential information to identify what is being described?

A restrictive phrase or clause plays a crucial role in providing essential information that identifies or clarifies the noun it describes. This type of phrase is necessary for the meaning of the sentence; without it, the sentence could become vague or its meaning might change significantly. For example, in a sentence like "The students who study hard will succeed," the phrase "who study hard" is restrictive because it specifies which students are being referred to—those who study hard. Removing this clause would leave the sentence less informative, as it would then refer to all students rather than a specific group.

In contrast, nonrestrictive phrases or clauses offer additional, non-essential information and can be removed from the sentence without altering its core meaning. Descriptive phrases may provide details but do not necessarily restrict or clarify the subject in the same essential way. Similarly, clarifying phrases can help explain concepts but do not always identify or restrict the noun being discussed. Therefore, the restrictive nature of the phrase ensures it is vital for understanding the context and specifics being conveyed.