Can the attributive clause everyone use that as the antecedent introductory word, or can we only use who or whom?

The grammatical rule governing the use of "that" versus "who" or "whom" with the antecedent "everyone" is prescriptively clear but practically flexible. "Everyone" is an indefinite pronoun referring to people, and traditional formal grammar dictates that pronouns referring to humans should be introduced by "who" or "whom" in attributive clauses, not "that." Therefore, according to this rule, "Everyone who attended the meeting" or "Everyone to whom the memo was sent" are considered correct, while "Everyone that attended" is often marked as less formal or even incorrect in strict editorial contexts. This distinction is rooted in a stylistic preference to anthropomorphize human antecedents with a specifically human relative pronoun, a convention more strongly upheld in edited prose and formal writing.

However, descriptive analysis of actual usage reveals that "that" is extensively and acceptably used with "everyone" in both spoken and written English, particularly in informal or less rigidly monitored contexts. The choice often hinges on register rather than grammatical correctness in a broader sense. In clauses where the relative pronoun is the object of a preposition, "whom" is the standard formal choice ("everyone for whom this is intended"), but it is frequently replaced by "that" or "who," or avoided altogether through syntactic restructuring in common usage. The mechanistic reason "that" is so prevalent is that it functions as a general-purpose relative pronoun for both animate and inanimate antecedents, and its use simplifies the speaker's or writer's decision-making process, bypassing the declining case distinctions between "who" and "whom."

The primary implication for writers and editors is one of stylistic judgment and audience expectation rather than absolute grammatical error. In academic, legal, or formal business writing, adhering to the "who/whom" convention aligns with the expected precision and conservatism of those genres. In journalistic, technical, or conversational English, "that" with "everyone" is generally unobjectionable and often goes unnoticed. The more significant point of potential confusion or error lies not in the choice between "that" and "who," but in the misapplication of "whom" for a subject or "who" for an object in formal settings where such a distinction is still expected. Ultimately, while "everyone who" remains the prescriptively safer choice for formal contexts, the blanket prohibition against "everyone that" is an oversimplification not supported by the reality of widespread, comprehensible usage across many dialects and registers of English.