"Rationale" refers to the underlying reason or explanation for something. It explains why something is done or believed in a certain way. Full definition
Indeed, settling on some kind of rationale for a new project is akin, he says, to pulling on your collar before serving in tennis. (twocoatsofpaint.com)
She really took the time to provide rationale behind every recommendation. (nicolejardim.com)
She provides rationale for the need for change in our current grading practices, as well as practical steps for implementation. (solutiontree.com)