Finally, in ancient times notes were not defined as they are to-day and their value was approximative only. This liberty in the execution of music is particularly perceptible in the works of Rameau. To conform to his intentions in the vocal part such music must not be interpreted literally. One must be governed by the declamation, and not by the written note indicating a long or short duration. The proof of this is to be seen when the violins and the voice are in unison--the way of writing them is different.
A great obstacle to executing ancient works from the eighteenth century on is in the interpretation of grace notes, "appoggiaturas" and others. In these cases there is an unfortunate habit in players of conforming to their own taste, which may guide a little, but cannot suffice in every instance. One can be convinced of this in studying The Method of Violin by the father of Mozart. We find there things which one would never dream of.
The "appoggiatura"[4] (from _appoggiare_, which in Italian means "to lean upon"), should always be long, the different ways in which it may be written having no influence upon its length. There is an exception to this when its final little note, ascending or descending, and preceding the larger note, is distant from it a disjointed degree. In this case it is not an "appoggiatura," and should be played short. In many cases it prolongs the duration of the note which follows it. It may even alter the value of the notes following.
I will cite in connection with the subject of the "appoggiatura" the beautiful duo with chorus of the "Passion According to St. Matthew," and at the same time, I would point out the error committed in making of this passion a most grandios performance with grand choral and instrumental masses. One is deceived by its noble character, by its two choruses, by its two orchestras, and one forgets that it was destined for the little Church of St. Thomas in Leipsig, where Sebastian Bach was organist. While in certain cantatas that composer employed horns, trumpets, trombones and cymbals, for the "Passion According to St. Matthew," he only used in each of the orchestras two flutes, two hautbois, changing from the ordinary hautbois to the hautbois d'amour and the hautbois of the chase,--now the English horn; that is to say, hautbois pitched a third and a fifth lower. These two orchestras and these two choruses then certainly were reduced to a very small number of performers.