All seventh chords use tertiary harmony (a stack of thirds). The main difference between major 7th and minor 7th chords lies in their third and top notes.
To create a minor 7th chord, lower both notes one fret to form a diminished chord – this method also works to produce dominant seventh chords.
Dominant 7th
Dominant seventh chords are an integral component of popular music, frequently being used to add tension or urgency, particularly within blues songs. One classic rock n’ roll hit such as Blue Suede Shoes is famously notable for utilizing them, using two dominant 7th chords as part of its toe-tapping melody.
Dominant 7th chords are formed from major triads with their seventh note flattened. Thus, these chords contain a root note, major third note and perfect fifth tone but their seventh can either be major (#7) or minor (b7) in character.
To create a dominant 7th chord, begin with a major triad and add a minor third on top. So for C7 we would use C, E, G and B as its components – instead of using a minor seventh we use major ninth to give more romantic sound to this chord.
Major 7th
Major 7th chords can be created by taking the root note of a major triad and adding an upper major seventh interval, creating a chord consisting of C, E, G and B notes. Since each major scale triad contains its own set of intervals that make up its chords, any seventh chord can easily be identified just by looking at its roots and chord.
This chord is one of the most frequently used 7th chords. Often referred to by its Roman numeral name of vi, it can be found across every key’s scale and makes an excellent way to start off songs with romantic, peaceful ambiance.
The major 7th is more dissonant than its dominant 7 counterpart and takes on more of a minor chord sound, making it popular choice for classical pieces containing free improvised sections like Verdi’s Aida where its opening chord is also major 7th based.
Minor 7th
Minor seventh chords can be formed from major triads by lowering its third and seventh intervals – for example, an E major 7th can be created by changing C and G (the third and seventh intervals respectively of the major triad) to C and B in its composition.
Minor 7th chords have a much darker sound than their major 7th counterparts and are frequently employed in jazz music, R & B and modern piano ballads – although this chord type may not be utilized as often in genres that utilize multiple triads such as rock music.
Minor 7th chords, also referred to as half-diminished sevenths, consist of a minor third, diminished fifth and minor seventh above the root note. They can be found both classical and romantic piano pieces as well as soul music. Furthermore, this kind of seventh chord adds tension by creating suspenseful feeling as well as anticipation in listeners.
Major 9th
Major 9 chords (commonly known as maj9) are major seventh chords with an extra ninth note added – effectively creating dominant seventh chords such as R-3-5-b7 + b9. These chords resemble minor 7 chords with their ninth added, similar to C7sus4 chords or C6/9 chords; however, the ninth note remains as an integral component.
A major 9 chord takes the emotional sound of a minor 7 and adds tension by adding an additional note, producing more tension with its added ninth note. Voiced shapes for major 9 chords may differ slightly than for their minor 7 counterpart, yet remain easy to learn.
To create a major 9 chord on guitar, simply add another minor third. That’s all there is to it.