Taxonomy of meanings for 何以:  

  • WHY
    • VPadVjustificationto what purpose? why?
    • VPadVrhetorical questionwhy on earth? surely for no good reason!
    • VPadVreasonfor what reason?; why?DS
  • HOW
    • PPadVquestionhow? by what means? (non-rhet.)
    • PPadVrhetorical questionhow? (i.e. no way!)
    • VPt(oN.)adSquestionBy what means am I going to do it? By what means is one going to do it?CH
    • VPadSquestion one is about to answer oneself: How? 何以知其然?CH