Strictly speaking the medieval signs and indicated that the melody is progressing inside a (fictive) "hexachord" of which the signed note is the "mi" or the "fa" respectively. That means they refer to a group of notes "around" the marked note, rather than indicating that the note itself is necessarily an accidental. For example, when a semitone relationship is indicated between F and G, either by placing a mi-sign () on F or a fa-sign () on G, only the context can determine whether this means, in modern terms, F-G or F-G, or even F–G. The use of either the mi-sign on F or the fa-sign on G means only that "some kind of F goes to some kind of G, proceeding by a semitone".