casuist

n. one who studies issues of moral conduct; false reasoning

Casuistry is an applied ethics term referring to case-based reasoning. Casuistry is used in juridical and ethical discussions of law and ethics, and often is a critique of principle-based reasoning.For example, a principle-based approach might conclude that lying is always morally wrong, the casuist would argue that, depending upon the details of the case, lying might or might not be illegal or unethical. For instance, the casuist might conclude that a person is wrong to lie in legal testimony under oath, but might argue that lying actually is the best moral choice if the lie saves a life. For the casuist, the circumstances of a case are essential for evaluating the proper response.
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Noun
1. someone whose reasoning is subtle and often specious
(synonym) sophist
(hypernym) reasoner, ratiocinator

n. casuist, one who studies issues of moral conduct; false reasoning

(v. i.)
To play the casuist.
  

(n.)
One who is skilled in, or given to, casuistry.