Mark fine distinctions and subtleties, as among words.

Roget 477: judge intuitively, judge by intuition; hazard a proposition, hazard a guess, talk at random.    reason ill, falsely etc. adj.; misjudge etc. 481; paralogize^†.    take on faith, take as a given; assume (supposition) 514.    pervert, quibble; equivocate, mystify, evade, elude; gloss over, varnish; misteach etc. 538^†; mislead etc. (error) 495; cavil, refine, subtilize^†, split hairs; misrepresent etc. (lie) 544.    beg the question, reason in a circle, reason in circles, assume the conclusion.    cut blocks with a razor, beat about the bush, play fast and loose, play fast and loose with the facts, blow hot and cold, prove that black is white and white black, travel out of the record, parler a tort et a travers [Fr.], put oneself out of court, not have a leg to stand on.    judge hastily, shoot from the hip, jump to conclusions (misjudgment) 481.    ... show more

Make more subtle or refined.

synonyms: rarefy, sublimate.

Roget 322: rarefy, expand, dilate, subtilize^†.   

Make (senses) more keen.

synonym: subtilise.