[42.]—Black notes, though of different lengths, may have the same note-head if they begin at the same time, the difference being shown in the hook or hooks:
Fig. 30.
But a whole note and a half note must have separate note-heads, since a stem would turn a whole note into a half note; and a whole note or half note and a quarter note must have separate note-heads, since a note cannot be white and black at the same time. In this case the note-head of shorter duration must be written first:
Fig. 31.
The rule is sometimes relaxed, and the longer note written first, when the shorter note is the first of a group.
Albeit a half note and an eighth, or other hooked note, may have the same note-head, provided this be that of the half note, because the hook shows that in one part the note is intended to be read as an eighth note. They cannot have an eighth note-head because there is nothing to distinguish the stem of a half note from that of a quarter:
Fig. 32.