Over time, some musical styles assimilated chord types outside of the common-practice style. In these chords, tones that might normally be considered nonchord tones are viewed as chord tones, such as the seventh of a minor seventh chord. For example, in 1940s-era bebop jazz, an F played with a C chord would be considered a chord tone if the chord were analyzed as C7(11). In European classical music, "greater use of dissonance from period to period as a result of the dialectic of linear/vertical forces led to gradual normalization of ninth, eleventh, and thirteenth chords [in analysis and theory; each additional non-chord tone above the foundational triad became frozen into the chordal mass."