Harmonizers who harmonise a scale often create chords in ascending thirds (three notes). If you have ever encountered a “I, IV, V” or ‘C major” progression then these are exactly the kinds of chords we are discussing here.
Chords can also be classified according to their harmonic function, which includes fundamental guitar chords, major and minor triads and dominant sevenths.
Triads
Triads are an easy and accessible starting point when it comes to chord formation. Triads consist of a root note, third note and perfect fifth above it that form an extremely stable structure due to all three notes being scale tones.
So the chords created from these scale tones will relate back to their scale of construction and be suitable for music written in that key.
Triads are typically named with Roman numerals to reflect their scale degrees of origin, as well as to signify whether the chord they create is major or minor in nature.
Once you understand all the triad shapes, they can easily be applied across the fretboard to quickly learn new chord shapes and gain an understanding of how chords relate on it.
Sevenths
After becoming proficient with major and minor triads, it’s time to explore sevenths. Seventh chords add depth, emotion, and complexity to a triad by including dissonant tones above its root note. Sevenths can be found across different genres of music but are especially prevalent in jazz, R&B/Blues music as well as film soundtracks.
As with triads, sevenths can also be classified by their intervallic content; however, sevenths composed on scale degrees other than 11 are uncommon as they destabilize a tonic triad by adding an unharmonious note that is neither harmonic nor part of the chord structure.
A typical dominant 7th is comprised of the root note and major third with minor seventh added on, in the form of an equation 1-3-5-7. Similar to triads, sevenths usually resolve via falling fifth (or rising fourth) root motion; however, they can also be combined with non-tertian chords such as augmented or diminished sevenths for chords such as Cmaj7 or Em7.
Extended Chords
Addition notes to chords is a key aspect of music theory. Chords featuring three or more distinct pitch classes are known as polychords; those comprising four pitch classes are called tetrachords; those comprised of five are pentachords; while chords comprising six pitch classes or more are known as hexachords.
Seventh chord extensions are the most frequently seen type, though any chord shape can benefit from such additions. Extension notes such as ninth, eleventh and thirteenth are commonly raised an octave from their root note to create chord extensions.
These chords may sound blocky and clunky, so they should generally only be used sparingly. But you don’t have to risk dissonance by using extended chords; often dropping the root note (for instance in Cmaj9 chord) reduces unwanted half-step “rubs” between chords for a more subtle sound in your progression.
Major and Minor Scales
Just as intervals are essential for chord building, scales play an integral part of scale composition. Every major key has an equivalent minor key with equal sharps or flats; this relationship is known as Relative Minor.
Minor keys always contain tonics that lie three half steps (or frets) below their respective Major tones, for instance A minor is the relative minor of C major.
Major and Minor Scales both feature whole steps and half steps arranged in different patterns; this makes minor scales sound melancholic or sorrowful when played aloud.
There are three categories of minor scales: natural minor, harmonic minor and melodic minor. All start on C and have the same scale degrees and solfege syllables as their Major counterparts but differ in how a flattened third gives each Minor scale its unique sound – for instance a chord such as C major/7th major/A minor is cheery when played using a Major scale but when performed using an A minor pentatonic scale its tone turns dark and melancholic.