Harmony

We have already learned that melody refers to pitches played in sequence. Harmony, on the other hand, deals with pitches sounded simultaneously. To put it another way, if melody is the horizontal element of pitch, then harmony is the vertical element of pitch.

Harmonies can be used to add support and depth to a melody, or sometimes harmony is simply the result of many melodies overlapping each other. Harmony is also important for the large-scale organization, or form, of musical works and can be used to give long pieces a sense of unity and structure.

Consonance and Dissonance

Some harmonies sound pleasing and stable, while others seem to clash and create a mood of tension and anxiety. The pleasing harmonies are called consonant, while the unpleasant harmonies are called dissonant. Each style of music has its own conventions about which harmonies are preferred, and these conventions are mostly determined by how consonance and dissonance are handled.

The perfect intervals (unison, octave, perfect 4th, and perfect 5th) are considered the most consonant intervals. The most dissonant intervals are a half step away from the perfect intervals: minor 2nd, major 7th, and tritone (also called augmented 4th or diminished 5th).

Dissonant harmonies can make listeners feel unsettled and tense. This tension makes listeners wish for the release and resolution of consonant harmonies. When dissonant harmonies change to consonant ones, it is called resolution. Longing for resolution can give music a sense of forward momentum, and the way that resolutions are granted or withheld can make listeners feel either satisfied or frustrated. Just as some stories are left unresolved, so are some harmonies.

examples of consonance and dissonance
examples of consonance, then dissonance

Chords

Chords are the basic units of harmony. A chord is an organized group of three or more simultaneous pitches. Any combination of pitches sounded simultaneously can be considered harmony, but chords are organized according to the intervals they contain and by the way they behave in relation to each other.

Triads

A triad is the most basic chord. A triad consists of three pitches (no more, no less) and is built by stacking major and/or minor thirds. The bottom note of a triad is known as the root, the middle one is the third, and the top one is the fifth.

The qualities of the thirds (major or minor) used to build a triad determine the quality of the chord itself. A major triad has a major third on the bottom and a minor third on the top, whereas a minor triad has a minor third on the bottom and a major third on the top. The interval between the lowest note and the highest note of a major or minor triad is a perfect fifth. A triad that consists of two minor thirds is a diminished triad, and the interval between the lowest and highest notes is a diminished fifth. A triad that uses two major thirds is an augmented triad, and the interval between the lowest and highest notes of this triad is an augmented fifth.

Major Triad Minor Triad Diminished Triad Augmented Triad
perfect fifth minor third perfect fifth major third diminished fifth minor third augmented fifth major third
major third minor third minor third major third
examples of major, minor, diminished, and augmented triads

Arpeggios

When the notes of a chord are played in sequence rather than simultaneously, we call this an arpeggio. Arpeggios are used in place of block chords (where all pitches are played simultaneously) in order to add rhythmic movement in a place that is harmonically static. Composers often give arpeggios to instruments that are not able to sustain pitches for a long period of time (examples: harpsichord, harp, guitar) because the pattern they create allows the same note to be sounded over and over again, giving the impression of a sustained pitch. This illusion of sustain allows the sequential pitches in arpeggios to imply a simultaneous chord.

example of arpeggios

Chord Terminology

In order to discuss the ways chords interact with each other, we must first give them names. If we begin with a major or minor scale, a triad can be built on each scale degree using the pitches that are available in that scale:

Just as the scale degrees are numbered, so are the chords built on these scale degrees. Instead of Arabic numbers (1, 2, 3...), we use Roman numerals (I, II, III...) to mark these chords. For major triads we use upper case (I, IV, V in major), for minor triads we use lower case (ii, iii, vi in major), for diminished triads we use lower case and a small circle (example: vii°), and for augmented triads we use upper case and a plus sign (example: VI+).

Notice that the chord built on the tonic note in a major scale is major, and in a minor scale it is minor.

Chords on scale degrees of a C major scale with Roman numerals
C major scale with chords and roman numerals
Chords on scale degrees of an A minor scale with Roman numerals
A minor scale with chords and roman numerals

Chord Progressions

A chord progression is a sequence of harmonies. Just as dissonant harmonies seem to want to resolve to consonant ones, chords often move in predictable patterns as well. The tonic pitch sounds like home in a scale or in a melody, and the tonic chord (I) sounds like the central and most restful harmony. Thus, the most common goal of a chord progression is to approach I. Once the tonic chord is achieved, that can be the end of a piece, or any chord can follow I to start another progression.

Common Patterns in Chord Progressions

The dominant chord (V) often preceeds I in chord progressions because it seems to have the strongest drive towards I. The large-scale motion from I to V and V to I creates the basis for a great deal of music in the Western world. On a small scale, however, there are other chords that can have dominant function and can be used instead of V to create variety. The most common substitution for V is vii°.

There are two chords that commonly preceed V (or vii°): ii and IV. These are called predominants. In jazz, ii is more common, whereas IV is more common in rock.

12-Bar Blues

One very common chord progression in popular music is the 12-bar blues. The harmonic pattern is quite simple: I-IV-I-V-I. To fill 12 measures (or bars) of music with these chords, the first I is repeated for the first four bars, then each of the remaining chords is used for two bars each:

Measure: 1 2 3 4 5 6 7 8 9 10 11 12
Chord: I I I I IV IV I I V V I I

This pattern may seem predictable and repetitive, but these features make the 12-bar blues a good framework for improvised solos, which are an important part of both jazz and rock. The blues genre and this blues progression were major influences in the development of both jazz and early rock 'n' roll. Here are some examples of songs that use the 12-bar blues:

Eric Clapton performing "Crossroads"

Cadences

Cadences are musical formulas that have developed by convention over time, and which function like grammatical punctuation. They involve the interaction of melody, harmony, rhythm, and meter, and usually mark the end of a phrase. Some cadences sound conclusive, complete, and resolved (like a period), while others sound incomplete (like a comma or colon). The most complete type of cadence is the full cadence, which moves from V to I. In a half cadence the progression is stopped on V, which makes it feel unfinished.

Sometimes composers will even start a cadential formula, but, instead of arriving at the cadence as expected, they will interrupt or change the formula with deceptive motion.

cadences