An Opinionated proposal written to sway the thinking of a greater establishment. Generally longer then your typical “Letter to the Editor,” or essay and are usually constructed carefully for the systematic attack on an issue. Many treatises begin with the chief arguments of the issues' detractors and continue on the discredit these arguments one by one.
Many great treatises have been written by people such as Theophrastus Bombastus von Hohenheim (on mining), Galileo (on the nature of the universe), Turing (on encryption), and Voltaire (on toleration).