Some words are used inappropriately. Many words are used inappropriately, confusing the reader. The writing is free or almost free of errors. There are occasional violations in the writing, but they don't represent a major distraction or obscure the meaning. The writing has numerous errors, and the reader is distracted by them.
Errors are so numerous that they obscure the meaning of the passage.
The reader is confused and stops reading. References to support claims are generally present. Although occasional references are provided, the writer overrelies on unsubstantiated statements. The reader is confused about the source of the ideas. References are not cited to support claims.