The principles of Gluck's school of operatic writing may be briefly
summarized as follows: That dramatic music can only reach its highest
power and beauty when joined to a simple and poetic text, expressing
passions true to Nature; that music can be made the language of all the
varied emotions of the heart; that the music of an opera must exactly
follow the rhythm and melody of the words; that the orchestra must be
only used to strengthen and intensify the feeling embodied in the
vocal parts, as demanded by the text or dramatic situation. We get some
further light on these principles from Gluck's letter of dedication to
the Grand-Duke of Tuscany on the publication of "Alceste." He writes: "I
am of opinion that music must be to poetry what liveliness of color and
a happy mixture of light and shade are for a faultless and well-arranged
drawing, which serve to add life to the figures without injuring the
outlines;... that the overture should prepare the auditors for the
character of the action which is to be presented, and hint at the
progress of the same; that the instruments must be employed according to
the degree of interest and passion; that the composer should avoid too
marked a disparity in the dialogue-between the air and recitative, in
order not to break the sense of a period, or interrupt the energy of the
action.... Finally, I have even felt compelled to sacrifice rules to the
improvement of the effect."

We find in this composer's music, therefore, a largeness and dignity
of treatment which have never been surpassed. His command of melody is
quite remarkable, but his use of it is under severe artistic restraint;
for it is always characterized by breadth, simplicity, and directness.
He aimed at and attained the symmetrical balance of an old Greek play.