An anacrusis (upbeat) is the beginning of a melody on a weak beat, before the first strong beat of a full measure. Such an “incomplete” initial measure seems to take a run-up, directing the motion toward the next strong accent, on which the main support of the phrase falls.
The anacrusis gives a melody a natural direction and breath — many famous themes begin precisely with one (from anthems to popular songs). It is closely linked to the prosody of speech: just as a word has an unstressed syllable before a stressed one, so in music the upbeat note “leads up” to the main one. The ability to feel the anacrusis correctly is critical for a performer: a wrongly “placed” beginning distorts the whole metric meaning of the phrase. The anacrusis is a subtle but fundamental element of musical expression.
