The Main difference between comparative vs contributory negligence is that comparative negligence seeks to compensate the injured party at least for some part of his or her damages or injuries, while contributory negligence is a total bar to any damage award to the plaintiff. For example:
John may be at fault but Sarah is also. In a contributory negligence state, Sarah has no case because she directly contributed to the injury by not looking before reaching for the bill.
In a comparative negligence state, a determination must be made as to how much each person contributed to the accident.
In a "pure" comparative state, if Sarah is 50% negligent, she can collect 50% of her damages.
In a "not greater than" or "not as great as" state, if Sarah and John are equally at fault, there is no case for either side.
In the slight vs. gross negligence state, Sarah also would have no case because negligence was equal.