All music, with the exception of recitative, is based on dance movement, i.e. each piece of music has a way that it uniquely moves. The composers are most of the time generous in giving a singer a few bars of musical introduction so that this movement becomes immediately apparent; one then takes a breath within the flow of this movement. However, a singer sometimes has to start the movement without benefit of an introduction; then it is imperative for the singer to feel the movement before taking the breath and then to take the breath, as always, within this movement.
Some piece of music maintain the same movement within the entire piece; others vary the movements within. Ask yourself: does the music of the piece I am performing move in two gestures within one bar? One movement per bar? One movement every two bars? The answer becomes immediately apparent when the movement exactly matches the mood and intention of the text being performed.
As an example, take the Neapolitan song 'O sole mio': try moving on each each eighth note; then, each quarter note; then one movement per bar; then one movement every two bars. Which is the appropriate movement? Feel the movement for each of these example by gently swaying back and forth. It's interesting how sometimes performers adopt the wrong movement for a piece, for example turning a lullaby into a march!
Questions? Discussion? Other examples?