Classification: Logician General’s Warning

Donald Byrd, School of Informatics and School of Music, Indiana University

rev. late January 2007


       Classification (in the ordinary way) is dangerous to your understanding.

      Classification ordinarily means hierarchic classification

      Hierarchic means subdividing cleanly into categories; often subcategories. But...

      Almost everything in the real world is messy

       Absolute correlations between characteristics are rare

       Example: some mammals lay eggs; some are “naked”

       Example: is the piano a keyboard, a string, or a percussion instrument?

       Example: Ginger Baker says Cream was “not really a rock group”

         People often say “an X has characteristics A, B, C, D…”

         They nearly always mean “an X has characteristic A [or B or C or…], and usually also A, C, D…”

       NB: most fundamental one may not be the one mentioned first

         Important special case: partitions (“flat” classifications, without subcategories)

       Example: “Is Bred still in love with Jan, or is he having an affair with Operetta?”

       Example: arguments against faster-than-light travel

         Messiness of the real world leads to:

       People who know better claiming absolute correlations

       Arguments among experts over which characteristic is most fundamental

       “Is it this or that or that?” questions that don’t have an answer

       Don changing his mind

         So should we abandon hierarchic classifications?

       Of course not: they're much too useful

       But be on your guard for misleading ones!




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Copyright 2006-07, Donald Byrd