1) Disingenuous reasoner 2) French word used in English 3) Quibbler of a sort 4) Ratiocinator 5) Reasoner 6) Resolver of moral dilemmas 7) Sophist 8) Specious debater 9) Specious reasoner 10) Student of morality 
• (v. i.) To play the casuist. • (n.) One who is skilled in, or given to, casuistry.
Cas'u·ist intransitive verb To play the casuist. Milton. Cas'u·ist noun [ Latin casus fall, case; confer French casuiste . See Casual .] One who is skilled in, or given to, casuistry. « The judment of any casuist or learned divine concerning the state of a man's soul, is not sufficient to give him confidence. South....
[n] - someone whose reasoning is subtle and often specious
sophist noun someone whose reasoning is subtle and often specious