What is the name of the seventh chord built on a major chord?

The name of the seventh chord built on a major chord is indeed Major 7th. This chord consists of a major triad (the root, major third, and perfect fifth) and an additional note—specifically, the major seventh above the root. The formula for constructing a Major 7th chord can be thought of as follows: take a major triad and add the seventh note from the major scale that corresponds to the root.

For example, in the case of a C Major 7th chord, you have the notes C (root), E (major third), G (perfect fifth), and B (major seventh). This gives the chord a harmonically rich and consonant sound.

In contrast, other types of seventh chords have their own specific characteristics. A Minor 7th chord includes a minor triad and a minor seventh, leading to a different sound. The Dominant 7th chord features a major triad with a minor seventh, often used in blues and jazz contexts. Finally, the Diminished 7th is built on a diminished triad with a diminished seventh, creating a tense and unstable quality. Understanding these distinctions highlights the unique qualities of a Major 7th chord and its role in music theory