An A or A- paper cannot have more than one error in punctuation, spelling, syntax, and grammar. The B paper is generally well-written but may have a few errors in punctuation, spelling, syntax, and grammar. The writer proof-read it, and caught almost all the glaring errors. The general organization of its argument is sound, but I may suggest moving a paragraph. The writer shows his control of the language, and I do not have to struggle to understand what he is saying.
Diction is good, the style is functional.
The C paper has more than three errors in errors in punctuation, spelling, syntax, and grammar. Its central thesis is unclear, or if it is clear, it is trite or obvious. This leads to problems of organization with concomitant problems in paragraph and sentence structure. As a result there is a good deal of red ink in the margins. If it is late two days it will be graded down a full grade , i.e. B to C. Beyond two days, don t bother.