Last time, we looked at the concepts of rhythm, melody and phrasing

This time, we’ll take a high-level look at harmony , scale, chord, and key

Harmony

Harmony is the sounding together of two or more musical sounds (e.g. two singers singing at the same time).  The term “harmony” is also used to describe the  particular choice of notes that make up a chord (see below).

Scale

In Western music, a scale typically contains 7 different pitches in an octave, which make specific intervals with the choice of scale start note.  Once that start note is determined, all the scale pitches must make the specified intervals with that start note.  Theory gives different sets of intervals different names, like “major” scale, or “harmonic minor” scale.  As Western music uses 12 semitones per octave, this means that one scale type can be built from 12 different start notes, and all their octaves can be used.  Different scale types will have different sets of intervals.  For example, the major scale must have pitches that make intervals with the start note of 0, 2, 4, 5, 7, 9 and 11 semitones, whereas the harmonic minor scale requires intervals of 0, 2, 3, 5, 7, 8 and 11 semitones.

There are also scales with 5, 6 and 8 pitches in an octave, and scales whose pitches cover two octaves.

Key

A key consists of a combination of scale type, and chosen start note.  For example, if we use the major scale, then C major and D major are different keys, as are C major an d C harmonic minor.

Chord

A chord is simply a combination of three or more different pitches played together.  These can be played melodically (“arpeggiated”), or all at the same time to create harmony.  The notes themselves may all be produced on one instrument, or produced by several instruments, such as bass and piano (or singers).

Many chords can be built using scale pitches, located at various semitones from a particular scale pitch (which may be the scale start note, or not).  For example, with the major scale, we could choose the pitches that make 0, 4, 7 and 11 semitones with its start note. This collection of semitones is also given a name in theory … in this case a “major 7th chord”.  We could build a chord starting at the second pitch in the scale, using pitches found at 0, 2 and 3 semitones from that second pitch, and so on.

Different progressions of chords from a key can make it obvious to the listener what that key is.