So I'm running through a brief history of church music for my middle school students, grades 6-8, and we've covered a bit of organum. I'll play some examples for them tomorrow and Tuesday, and it's very much rekindled my own interest in the stuff, Perotin and Leonin. I had forgotten how simple, devotional, and genuinely prayerful this music is. I found this lovely quote on Wikipedia from John of Salisbury, Bishop of Chartres in the 12th century. He was writing about the music he had heard at Notre Dame, likely composed by Messrs. Leonin and Perotin:

"When you hear the soft harmonies of the various singers, some taking high and others low parts, some singing in advance, some following in the rear, others with pauses and interludes, you would think yourself listening to a concert of sirens rather than men, and wonder at the powers of voices … whatever is most tuneful among birds, could not equal. Such is the facility of running up and down the scale; so wonderful the shortening or multiplying of notes, the repetition of the phrases, or their emphatic utterance: the treble and shrill notes are so mingled with tenor and bass, that the ears lost their power of judging. When this goes to excess it is more fitted to excite lust than devotion; but if it is kept in the limits of moderation, it drives away care from the soul and the solicitudes of life, confers joy and peace and exultation in God, and transports the soul to the society of angels..."

find it here, under the heading Contemporary Critiques: http://en.wikipedia.org/wiki/Perotin

How wonderfully put! How accurate the description of the power of music to lull the heart or stir the passions!