Which one is correct?
- He runs less fast than I.
- He runs less faster than I.
closed as general reference by TimLymington, Jon Hanna, tchrist, MετάEd, Carlo_R. Feb 22 '13 at 0:07
This question is too basic; it can be definitively and permanently answered by a single link to a standard internet reference source designed specifically to find that type of information. If this question can be reworded to fit the rules in the help center, please edit the question.
"Faster" is already a comparative, so to add another comparative "less" onto it would be incorrect.
However, why not just use "slower"? "Less fast" sounds awkward even if it is technically grammatically correct.