Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             reactive intermediates
               Class cations [X+]
                 1 Class carbocations
                 2 Class onium compounds
                 3 Class arenium ions
                 4 Class amidium ions
                 5 Class sulfenylium ions [RS+ (R≠H)]