There's a number of methods. Politics is one method. Science is
   another method. Negotiations. Conversations. Comparing.
   Relating. - The flaw however, is in your original question.
   Reasoning: "the action of thinking about something in a logical,
   sensible way." Ok. What's logical? Is it a system from the 19th
   century? It could be. It doesn't have to be. What's sensible?
   See the problem? It goes around and around. The scientific
   method is *a way". But it's fallacious to believe "a way" is
   "The Way". For example, the Sciences work terribly in a court
   situation. They're fine for supporting evidence - and evidence
   in a court hearing is *different than* what's considered
   evidence in the sciences, even if there is much overlap. Can you
   use any of the Sciences to determine intent? What about a
   "reasonable sentencing"? It's consensus of some sort. Within the
   Sciences, it is also a matter of consensus. It's a special KIND
   of consensus uniquely suitable for its purposes.