Measured against human writing
These come from published corpus comparisons. They are the strongest evidence on this page, and they still have limits: The Economist measured news journalism, and the Reinhart figures are from 2024 models.
Long, noun-heavy vocabulary
"the implementation of", "utilization", "significant", "increasingly"
Polysyllables, Latinate suffixes, and nouns made from verbs. All four models in the study do it; Gemini and Claude do it most. Reinhart et al. put nominalisations at 1.5 to 2 times the human rate.
Rule in the skill: Use the plain verb and the common word. Source: The Economist, "How to Spot AI Writing", 30 July 2026.
Long sentences chained with "and"
"And" is the most overused word in the study, and paragraphs are rarely broken by a short statement.
Rule in the skill: Let sentence length follow the content. Source: The Economist, "How to Spot AI Writing", 30 July 2026.
Thin punctuation
Fewer commas and semicolons than human writers, and almost no parentheses.
Rule in the skill: Put asides in commas or parentheses. Source: The Economist, "How to Spot AI Writing", 30 July 2026.
"Not X but Y", "not only but also", and lists of three
"It's not just a defensive measure — it's a foundational component."
ChatGPT and Claude use these most per 1,000 sentences.
Rule in the skill: Deny X only when this reader is likely to believe X. Source: The Economist, "How to Spot AI Writing", 30 July 2026.
The trailing "-ing" clause
"..., underscoring its importance"
Measured at 2 to 5 times the human rate. It attaches significance to a fact without giving evidence for it.
Rule in the skill: Make claims specific and checkable. Source: Reinhart et al., PNAS, 2025.
The em dash, in Claude only
Of the four models, only Claude uses more em dashes than human writers. ChatGPT uses fewer than any other writer in the study. The article gives no figure for the size of the gap.
Rule in the skill: Use an em dash only for a break that a comma would hide. Source: The Economist, "How to Spot AI Writing", 30 July 2026.
No quoted experts
"studies show", "experts say"
The models do not quote named people.
Rule in the skill: Replace "experts say" with the fact and who said it. Source: The Economist, "How to Spot AI Writing", 30 July 2026.