The Harmonic technique or Recognition Signal is designed to assist in creating the feeling of harmony in the souls of the listener and the person talking. Human beings will produce this "technical" utterance when acknowledging or agreeing with the person talking. The harmony between speaker and listener results from this utterance. The absence of this utterance indicates a failure to communicate or to persuade. The technique is most effective when the speed and manner of executing it is closest to a spoken technique.
The recognition signal in human speech is designed to express many things from the listener's point of view...agreement, the ability to follow a line of reasoning, "please continue," assent to a point made, etc. It is sounded: uh-huh, with the pitch rising at the end. It is interesting to note that in section X of his Poetics, Aristotle defines recognition as "a change from ignorance to knowledge." When listeners hear the recognition signal expressed in music, it creates the feeling in the listener of being able to easily follow what is happening in the music and the feeling of unanimity between the performer and the listener. It also makes knowing what the harmony of a note is with utter clarity. The recognition signal or cercare is the vehicle whereby the feeling in the listener of not knowing what is happening in a piece of music is changed into a feeling of knowing what is happening. That feeling is usually articulated as being spiritual because it is experienced as a feeling of being enlightened.
It is extremely interesting that the word "cercare" (pronounced chair-cár-e), from the quote from the Griepenkerl letter, (that "Bach himself, his sons, and Forkel performed the masterpieces with such a profound declamation that they sounded like polyphonic songs sung by individual great artist singers; all means of good singing were thereby brought into use. No cercare, no portamento was missing. There was even breathing at the right places...Bach's pieces want to be sung with the maximum of Art."), is defined in Riemann's Musiklexicon as a 17th century Italian ornament in which the upper or lower auxiliary note is performed softly and suddenly to the main note. This is exactly how the recognition signal is expressed. In otherwords, the recognition signal is a cercare. Yet, today the cercare is frowned on as being in exceedingly bad taste by classical music singers. Do you suppose Bach played his own music in bad taste? Who do we trust in this matter? We choose to trust Bach and natural human expression.
Application: The speed of the Cercare is its most important characteristic. If the speed of the cercare is too slow then it sounds like an arpeggio. If the speed is too fast, then it sounds like a grace note. The correct speed for most uses is the speed at which you most naturally would say "pah-dum" with the accent on the second syllable. If you say this as pah dum with the accent on the first syllable, it is too slow. And, if you say it as pahdum without accent, it is too fast. As the music expresses greater gravity of feeling, the cercare is performed more slowly and with greater emphasis. As the music expresses more liveliness, the cercare is performed more rapidly and lightly.
Bach's statement of the Chaconne from the D minor violin Partita is really just one big excuse for playing one cercare after another. The Italian concerto by Bach begins with a cercare. Beethoven's Pathetique sonata begins with a cercare followed by another with a few notes stuck in between. The 9th Symphony of Beethoven is full of cercare...though you would never know it from hearing it as it it usually played.