Dissonance vs. Consonance

Megan mentioned in our presentation on music that early polyphony was usually large, "consonant" intervals (separation between tones).  If you have a piano, you can demonstrate consonant intervals by holding some combination of the C, E, and G keys (with which you can make a perfect 5th, a perfect 4th, a major third, a minor third, or a perfect octave).  The Ave Maria chant we listened to, for example, consisted only of such intervals--the notes did not ever clash at all.  Later music, however, displays a steady trend toward more and more dissonant intervals; that is, close intervals like the minor second (B and C is an example on the keyboard) or various seventh intervals (like A and B).  Such intervals have a much harsher sound.  A good example of this trend taken to an extreme is the music of Sergei Prokofiev (1891-1953), the composer of, among other things, Peter and the Wolf.  Here's a recording of his Diabolic Suggestion:

This is a very different style of composition.  I think it represents a much broader trend throughout music, the arts and philosophy away from ideals and naïveté and towards a more cynical and realistic approach.  This trend is very old; we saw it, for example, in the transition from the simplistic, idealized kuoros to more complicated Hellenic works.  To extend it to its extreme à la Prokofiev, we have more modern artworks like Duchamp's Fountain and Salvador Dalí's Chien Andalou, which are similarly grotesque and morbid.  I suppose that as society gets more tired and complicated, people become disillusioned and this disillusionment gets reflected in art.