Expression was introduced into music by the chord of the dominant seventh, the invention of which is attributed to Monteverde. However, Palestrina had already employed that chord in his "Adoremus," but probably without understanding its importance or divining its future.
Before this invention the interval of three whole tones (Triton) was considered an intolerable dissonance and was called "the devil in music." The dominant seventh has been the open door to all dissonances and to the domain of expression. It was a death blow to that learned music of the sixteenth century; it was the arrival of the reign of melody--of the development of the art of singing. Very often the song or the solo instrument would be accompanied by a simple, ciphered bass, the ciphers indicating the chords which he who accompanied should play as well as he could, either on the harpsichord or the theorbe. The theorbe was an admirable instrument which is now to be found only in museums,--a sort of enormous guitar with a long neck and multiple strings which offered great opportunities to a skilful artist.
It is curious to note that in ancient times there was not attributed to the minor and major keys the same character as is assigned them to-day.[2] The joyous canticle of the Catholic church, "O Filii et Filiæ," is in the minor. "The Romanesca," a dance air of the sixteenth century, is equally in the minor, just like all the dance airs of Lully, and of Rameau, and the gavottes of Sebastian Bach. The celebrated "Funeral March" of Haendel, reproduced in many of his works, is in C Major. The delicious love duo of Acis and Galathee, which changes to a trio by the addition of the part of Polyphemus, is in A Minor. When Galathee weeps afterward over the death of Acis, the air is in F Major. It is only recently that we find dance airs in the major mood or key.
From the seventeenth century on, music entered into everyday life, never again to be separated from it. Thus music has remained in favor, and we are continually hearing executed the works of Bach, of Haendel, of Hayden, of Mozart and of Beethoven. How are such works executed? Are they executed as they should be? That is another question.
One source of error is found in the evolution which musical instruments have undergone. In the time of Bach and Haendel the bow truly merited its Italian name of "arco." It was curved like an arc--the hairs of the bow constituted the chord of the arc, a very great flexibility resulting which allowed the strings of the instrument to be enveloped and to be played simultaneously. The bow seldom quitted the strings, doing so only in rare cases and when especially indicated. On this account it happens that the indication of "legato" is very rare. Even though there was a separate stroke of the bow for each note, the notes were not separated one from the other. Nowadays the form of the bow is completely changed. The execution of the music is based upon the detached bow, and although it is easy to keep the bow upon the strings just as they did at the commencement of the nineteenth century, performers have lost the habit of it. The result is that they give to ancient music a character of perpetually jumping, which completely destroys its nature.