rationalize vs thresh out

rationalize

verb
  • To remove radicals, without changing the value of an expression or the roots of an equation. 

  • To make something rational or more rational. 

  • To justify an immoral act, or illogical behaviour. “The process of thought by which one justifies a discreditable act, and by which one offers to oneself and the world a better motive for one's action than the true motive” 

  • To structure something along modern, efficient and systematic lines, or according to scientific principles. This often includes eliminating duplication and grouping like or similar items. 

thresh out

verb
  • To extract or remove by threshing. 

  • To thrash out. 

How often have the words rationalize and thresh out occurred in a corpus of books? (source: Google Ngram Viewer )