Most textbooks name these chords formally by the type of triad and type of seventh hence, a chord consisting of a major triad and a minor seventh above the root is referred to as a major/minor seventh chord.

'A ranking by frequency of the seventh chords in C major would be approximately that shown.' Additionally, the general acceptance of equal temperament during the 19th century reduced the dissonance of some earlier forms of sevenths.

As time passed and the collective ear of the western world became more accustomed to dissonance, the seventh was allowed to become a part of the chord itself, and in some modern music, jazz in particular, nearly every chord is a seventh chord. The seventh destabilized the triad, and allowed the composer to emphasize movement in a given direction. In its earliest usage, the seventh was introduced solely as an embellishing or nonchord tone. However, a variety of sevenths may be added to a variety of triads, resulting in many different types of seventh chords. When not otherwise specified, a 'seventh chord' usually means a dominant seventh chord: a major triad together with a minor seventh. A seventh chord is a chord consisting of a triad plus a note forming an interval of a seventh above the chord's root.

B flat minor 7th chord