finally gives way to after the cadential six-four at the beginning of the final bar. It is usual for most of the piece to occur between the primary tone and the final descent to .

This long prolongation of demonstrates an important theoretical concept connected with the fundamental structure which Schenker calls 'mental retention'.

He proposed that once we have heard a structural note, we hold it in our minds until the establishment of the next one. In "Three Blind Mice", the first note of the fundamental structure is held in our minds until the final . In this case, no note of equivalent structural importance contradicts it - there is no large-scale prolongation of a note from a harmony other than the tonic.

Even if there were, for example, an F neighbour note prolonged over several bars, the principle of mental retention suggests that we would hear the next E over the tonic as a return to the original - this scale degree being held in our minds for the whole of the neighbour note diminution.

As with many of Schenker's most important concepts, mental retention occurs both on the smallest level (e.g. the B neighbour note in bar five) and the largest. In "Three Blind Mice", the effect is easily perceptible but the mental retention of the primary tone across the first movement of a Beethoven symphony, for example, is arguably more conceptual than perceptual.