reason

[1]	think , reason out , conclude , conclude , calculate , reckon , estimate , figure (out) , work out , deduce , act/think rationally/logically , ratiocinate , use (one's) judgement/common sense , use (one's) head , put two and two together
[2]	reason with , argue , argue with , remonstrate with , debate with , discuss with , talk over with , plead with , convince , persuade , dissuade , urge , prevail upon

[1]	ground , justification , argument , case , explanation , rationale , ground(s) , pretext , vindication , defence , why (and wherefore) , (Literary) apologia , apology
[2]	judgement , common sense , intelligence , sanity , sense(s) , saneness , insight , perspicacity , percipience , understanding , rationality , reasoning , mind , intellect
[3]	purpose , understanding , intellect , aim , intention , object , objective , goal , motive , end , point
[4]	excuse , rationality , reasonableness , rationalization
[5]	by reason of , cause , grounds , because of , on account of , owing to , by virtue of , as a result of , due to
[6]	within/in reason , reasonable , sensible , justifiable , rational , fitting , proper , acceptable