Why Do Ai Grammar Checkers Flag ‘they/them’ Pronouns As ‘inconsistent’ In Formal Documents

It’s a quiet but increasingly common frustration: you write “Each student must submit their assignment by Friday,” hit “Check Grammar,” and watch your AI tool underline their with a red squiggle labeled “pronoun-antecedent disagreement.” The suggestion? Replace it with “his or her” — or worse, “his/her.” You know better. You’ve read the APA, MLA, and Chicago style guides. You’ve seen “they” endorsed by the Associated Press and Merriam-Webster. Yet the software insists it’s “inconsistent.” What’s really happening isn’t a grammatical error — it’s a collision between linguistic evolution and algorithmic legacy.

This isn’t about ignoring grammar rules. It’s about understanding why today’s most widely used AI writing assistants — from Grammarly and ProWritingAid to Microsoft Editor and Google Docs’ built-in checker — still treat singular “they” as suspect in formal contexts. More importantly, it’s about equipping yourself with the knowledge to respond intelligently: when to accept the flag, when to override it confidently, and how to shape your writing so it satisfies both human readers and machine validators — without compromising inclusivity, clarity, or professional credibility.

The Historical Grammar Rule That Still Powers Today’s Algorithms

Most AI grammar checkers rely heavily on rule-based parsing engines trained on decades of formal English corpora — legal briefs, academic journals, government reports, and 20th-century textbooks. In those sources, “everyone,” “anyone,” “each,” and “nobody” were almost always paired with “he,” “him,” or “his” — not because that was linguistically superior, but because prescriptive grammar manuals from the 18th and 19th centuries codified masculine generics as standard. These rules persisted long after usage had shifted.

Modern NLP models inherit these patterns. When trained on text where “Each applicant must verify his identity,” appears 12,000 times and “Each applicant must verify their identity” appears only 372 times (and mostly in informal email corpora), the model learns statistical association — not semantic validity. Its “inconsistency” flag doesn’t mean “this violates English grammar”; it means “this pairing occurs rarely in my training data for formal registers.” That distinction is critical — and routinely misunderstood.

The irony deepens when you consider that singular “they” has been used continuously in English since the 14th century. Chaucer used it. Shakespeare used it. Austen used it. The Oxford English Dictionary’s earliest citation is from 1375 (William and the Werewolf). What changed wasn’t the pronoun — it was social awareness, and with it, the urgency to use language that affirms gender identity without defaulting to binary assumptions.

Why Formal Documents Trigger the Flag More Often

AI tools don’t apply grammar rules uniformly. They layer register detection — an estimation of whether your text reads like a legal contract, a peer-reviewed paper, or a Slack message — atop syntactic analysis. Formal documents trigger stricter adherence to legacy conventions for three interlocking reasons:

1. Register-weighted confidence scoring: If the model detects passive voice, nominalizations (“utilization” instead of “use”), Latin-derived vocabulary, and low-frequency conjunctions (“furthermore,” “notwithstanding”), it downweights variants associated with informal or conversational speech — including singular “they.”
2. Antecedent specificity bias: Checkers are especially wary when the antecedent is indefinite (“someone,” “a user”) or quantified (“every,” “each”). They conflate grammatical number (singular noun) with pronoun agreement expectations — ignoring that English has long allowed semantic agreement over strict morphological agreement in such cases.
3. Style guide fragmentation: While APA (7th ed.), MLA (9th ed.), and Chicago (17th ed.) explicitly endorse singular “they” for unknown or nonbinary antecedents, some corporate style guides, older legal drafting manuals, and internal compliance templates still prohibit it. AI tools trained on mixed sources reflect this inconsistency — not as ambiguity, but as “error.”

This explains why “Alex forgot their keys” might pass unflagged in an email draft, while “Every employee must update their emergency contact information” triggers a warning in a company HR policy document. The sentence structure is identical — the context shifts the tool’s tolerance threshold.

When the Flag Is Legitimate — And When It’s Not

Not all “they/them” flags are misguided. Some signal real ambiguity or stylistic weakness. Others reflect outdated assumptions. Knowing the difference requires looking beyond the red underline.

Here’s how to evaluate the warning using concrete criteria:

The key insight: “Inconsistency” is often a proxy for “I can’t resolve the reference cleanly” — not “this violates English.” When the tool can’t confidently map “they” back to a single antecedent (due to distance, intervening clauses, or competing nouns), it defaults to caution. That’s a limitation of parsing depth — not evidence of incorrect usage.

A Real-World Revision Workflow: From Flagged to Flawless

Consider Maya, a compliance officer drafting a new remote-work policy for a 2,400-person tech firm. Her first draft included: “Each remote employee must secure their home network against unauthorized access.” Grammarly flagged “their” as inconsistent. She didn’t ignore it — nor did she revert to “his or her.” Instead, she followed this four-step revision protocol:

1. Analyze the antecedent: “Each remote employee” is singular, indefinite, and gender-neutral. Singular “they” is the standard, inclusive, and grammatically accepted solution.
2. Check style alignment: Her company’s communications style guide explicitly references APA’s endorsement of singular “they” for inclusivity and concision. No internal policy forbade it.
3. Test alternatives: “His or her” added syllables without value and excluded nonbinary staff. “His/her” looked unprofessional. “Their” was cleaner, kinder, and clearer.
4. Add context-aware justification: In the document’s “Style Notes” appendix, she added: “We use singular ‘they’ to refer to individuals of unspecified or nonbinary gender, per APA 7th edition and internal DEIB standards.” This preempted future reviewer objections.

The final version stood — and passed legal review. More importantly, employees reported the language felt more respectful and easier to parse than earlier drafts burdened with clunky workarounds. Maya’s workflow turned a friction point into a quiet act of leadership.

Expert Insight: Linguists vs. Language Models

“Grammar checkers mistake frequency for correctness. Just because ‘he or she’ appeared more often in mid-20th-century legal writing doesn’t make it grammatically superior — it makes it historically contingent. Singular ‘they’ meets every criterion for standard English: it’s rule-governed, widely understood, consistently used across dialects, and actively taught in composition courses. When AI tools flag it, they’re revealing their training data’s blind spots — not the writer’s error.”
— Dr. Lena Torres, Sociolinguist and Director of the Center for Writing & Rhetoric, University of Michigan

Dr. Torres’ point cuts to the core: grammar is descriptive, not just prescriptive. It evolves through use — and AI tools lag behind that evolution by years, sometimes decades. A 2023 study in Corpus Linguistics and Linguistic Theory analyzed 1.2 billion words of formal U.S. English (2010–2022) and found singular “they” increased 240% in academic and policy writing — yet commercial grammar checkers showed only a 12% reduction in false-positive flags over the same period. The gap isn’t narrowing fast enough.

Practical Action Plan: Working With (Not Against) Your Tools

You don’t need to abandon AI checkers — you need to use them with intention. Here’s a realistic, field-tested checklist for writers, editors, and communicators who value both precision and inclusion:

• ✅ Disable “gender-neutral pronoun warnings” in your tool’s settings (Grammarly: Settings > Writing Suggestions > toggle off “Use gender-neutral language” if it overrides valid “they”)
• ✅ Create custom style guide snippets in tools that support them (e.g., ProWritingAid’s “Custom Style Guide” lets you add “Singular ‘they’ is acceptable for indefinite antecedents” as an approved exception)
• ✅ Run two passes: First with grammar checking on, noting all “they” flags; second with grammar off but spell-check on, focusing solely on clarity and flow
• ✅ For high-stakes documents, add a brief “Language Note” to your editor or stakeholder explaining intentional singular “they” usage — it prevents rework and signals editorial rigor
• ✅ When forced to revise for conservative audiences, use plural antecedents (“Employees must secure their networks”) instead of reverting to “he or she” — it’s more natural and avoids gender assumptions entirely

FAQ: Addressing Common Concerns

Is singular “they” really accepted in formal writing — or is that just progressive opinion?

It’s formally accepted by every major U.S. and U.K. style authority: APA, MLA, Chicago, AP, Oxford, and the U.K. Government Digital Service. The American Dialect Society named singular “they” its Word of the Year in 2015 and 2019. Acceptance isn’t ideological — it’s empirical, based on centuries of usage and contemporary corpus analysis.

Won’t using “they” confuse readers about number or meaning?

No — context resolves number instantly. We understand “Someone left their coat” as singular because “someone” is singular. English relies on semantic cues far more than morphological ones (compare “The news is good” vs. “The headlines are good”). Studies show readers process singular “they” as quickly and accurately as gendered pronouns — and with higher comprehension when gender is irrelevant to the point.

If AI tools keep flagging it, does that mean I shouldn’t use it in client-facing documents?

Not at all — but do so deliberately. Flagging is a signal to double-check, not a command to delete. In client work, briefly annotate your choice (“Per APA 7, singular ‘they’ used for inclusivity and concision”) in comments or a style note. Clients respect informed decisions far more than blind compliance — and increasingly, they expect inclusive language as baseline professionalism.

Conclusion: Write With Authority, Not Apology

That red squiggle under “their” isn’t a verdict. It’s an invitation — to pause, to assess, to choose consciously. It asks you to decide whether you’re writing for a 1950s textbook, a 2024 team charter, or something in between. The most skilled writers today don’t just obey grammar tools — they interrogate them. They know when “they” strengthens clarity, affirms identity, and aligns with institutional values. They also know when recasting a sentence (“All employees must secure their networks”) sidesteps the issue entirely — and when holding the line on “Each employee must secure their network” advances both language and equity.

You don’t need permission to use singular “they” correctly. You need confidence rooted in evidence — not algorithms trained on yesterday’s norms. So next time your checker objects, take a breath. Open your style guide. Recall Chaucer, Austen, and the thousands of professionals who use “they” daily in boardrooms and courtrooms. Then click “Ignore” — or better yet, “Explain why this is correct” — and move forward with precision and purpose.