Answer:
The method of counterexample in ethical reasoning is used to assess the plausibility of general ethical principles.
The key idea is that if we can find a compelling counterexample to a proposed ethical principle - a case where following that principle would lead to a clearly unethical outcome - then it casts doubt on the validity of the principle.
For example, consider the principle "it is always wrong to lie." A counterexample could be a case where lying is the only way to save an innocent life, such as lying to a murderer about the whereabouts of their intended victim. Most would agree that lying is ethically correct in that case, which shows the proposed principle is too broad.
The method aims to refine and improve our ethical principles by revealing exceptions and limitations. The other options are related but distinct:
Assessing the plausibility of specific ethical judgments about particular cases
Assessing the plausibility of ethical conclusions derived from arguments
Assessing the overall plausibility of an ethical argument
So in summary, the main purpose of counterexamples is to test general principles, not specific judgments, conclusions, or full arguments. It's a way to probe the boundaries of ethical rules and develop more robust guidelines.