Common Mistakes in AI-Generated Texts: A Practical Guide for Editors

By David Hawthorne · OneThorn Copy Editing Services

Artificial intelligence has become a valuable writing partner, accelerating drafting and reducing the friction of getting words on the page. Yet AI-generated prose still requires a discerning human eye. While generative models can produce fluent, coherent language at impressive speed, they routinely fall into predictable traps.

The following sections outline the most common problems found in AI-generated writing, spanning grammar, punctuation, factual reliability, structure, and stylistic consistency.

Grammar Errors That Slip Through

AI writing is often grammatically sound at the sentence level, but subtle errors appear with surprising regularity—especially in longer passages.

1. Tense Drift

AI systems occasionally shift verb tenses mid-paragraph. A passage may open in the present tense, drift into the past, then revert without narrative or logical justification.

2. Subject–Verb Agreement in Complex Sentences

Long sentences with interrupting clauses can cause agreement errors, such as “The series of reports are complete” instead of “…is complete.” Models lose track of the actual subject when multiple nouns intervene.

3. Overextension of Parallelism

AI-generated lists often begin in one grammatical form and end in another, creating awkward or uneven phrasing.

4. Missing or Misused Articles (“a,” “an,” “the”)

Generative models frequently omit articles or choose the wrong one, especially with abstract or technical nouns. The result is prose that feels clipped or faintly non-idiomatic.

Punctuation Problems: Small Marks, Big Consequences

Punctuation is one of the fastest ways for experienced editors to detect machine-generated text.

1. Em Dash Spacing Inconsistency

AI writing frequently alternates between “—like this” and “— like this” within the same document.

2. Overuse and Underuse of Commas

• Overuse: Unnecessary commas disrupt rhythm and dilute emphasis.
• Underuse: Missing commas create ambiguity and rushed prose.

3. Mechanical or Redundant Punctuation

Repeated em dashes, parentheses, or colons often feel mechanical rather than intentional.

Factual Hallucinations: When Plausibility Replaces Truth

One of the most dangerous flaws in AI-generated writing is hallucination—the confident fabrication of facts, sources, or relationships that do not exist.

Because generative systems optimize for linguistic plausibility rather than accuracy, invented details can pass unnoticed into published work, undermining credibility and trust.

Structural Weaknesses in AI-Generated Prose

Even when individual sentences are clean, AI-generated documents often suffer from predictable structure, filler-heavy paragraphs, and forced transitions.

Stylistic and Voice Inconsistencies

AI text can appear polished at first glance, yet shifts in tone and voice often reveal its origins.

How These Patterns Add Up

AI tools accelerate drafting, but they do not replace editorial judgment. Understanding these recurring weaknesses allows editors to refine AI-assisted writing until it reads with authority, precision, and purpose.