Thus "I" describes the tonic chord, the chord built on the tonic note, at a given time.
The second step is implementing these modes as chords built on a common root.
In some contexts an arabic number, or careted number, may refer also to a chord built upon that scale degree.
Few composers seemed to question whether chords built by other means were possible.
The harmony of this section is based on a 12-note chord built from major seconds and perfect fourths.
The foundation is the most important note and chords built are almost always in root position.
In western classical notation, chords built on the scale are numbered with Roman numerals.
Thus, a major chord built upon C is called a C major chord.
On this understanding, the diminished seventh chord built on the leading note is accepted as diatonic in minor keys.
Other chords built on these, such as ninth chords, often include tritones (as diminished fifths).