Sometimes some non harmonic notes are causing troubles inside the perfect triad. Non harmonic notes are not part of the chord and appear as dissonances in need of preparation in the previous chord and especially, a resolution in the next chord. In tonal harmony, non harmonic notes are six in number: The retardation, the appoggiatura, the passing tone, the neighbourg tone, the anticipation and the echappée. To illustrate these examples, we choose a basic chord progression that begins on the tonic chord I, through the dominant chord V and returns by a perfect cadence, in the tonic chord I. As seen here on the G dominant seventh chord G B D F in the tonality of C major, the note "E" is not part of the chord, and is dissonant. It is prepared by a slur in the previous chord and resolved by step in the following chord on the note "D" actual fifth of the dominant seventh chord. Note "E" is the upper retardation of real note "D" . The retardation therefore need 3 phases which are: the preparation phase in the previous chord, the dissonance phase or "retardation", and the phase of "resolution" in the following chord. With the appoggiatura, the principle is the same, but it has not to be prepared in the previous chord. So it is a note played on the beat and resolved by step into the next chord. Struck on time, the appoggiatura has a more expressive character that the retardation. The passing tone is a melodic note which provides a transition between the note before and the following note. For example here, the note "E" is a bridge between the previous "F" and the following "D". The passing tones are always proceeding by single step. The neighbourg tone is an ornamentation of real note of the chord and remain a non harmonic note. In this example, the note "D" (fifth of dominant chord) is repeated on the fourth beat and is ornamented by a "E" note. The anticipation, as the name suggests, anticipates a note of the next chord. In this example, the note "C" located on the fourth beat is not part of the dominant chord, but it anticipates the note "C", real tonic for the next chord. Unlike previous non harmonic notes, the echappée is neither part of the dominant chord or the following tonic chord. It is not proceeding by step in regards with the previous and following notes.