Two or more notes sounding together are known as a chord.
A triad is a chord of three notes. For example, C - E - G is the C major triad. C is the root note, E is the third - an interval of a third above the root - and G is the fifth - an interval of a fifth above the root.
In any major key, the chords built on the first, fourth and fifth degrees of the scale are all major. In the key of C, these are the chords of C, F and G. They are also sometimes called I, IV and V (for first, fourth and fifth in Roman numerals), or primary triads.
The chord built on the first note of the scale, I, is called the tonic. The chord built on the fourth, IV, is called the subdominant and the V is called the dominant.
All the chords built on other notes in the scale of C are minor, except chord VII - the notes B – D – F, which is diminished.
When a seventh is added to a chord this is known as a seventh chord. The dominant seventh of a V chord can be shown by the symbol V7.
For example, G7 is made by taking the major triad of G (G - B - D) and adding an F (G - B - D - F).
A cadence is formed by two chords at the end of a passage of music.
Sometimes the final cadence of a piece in a minor key ends with a major chord instead of the expected minor. This effect is known as a Tierce de Picardie.
The video shows examples of different types of cadence.
The character of a piece of music is related to its key centre or tonality:
Two common modes are the Dorian mode and the Mixolydian mode. Modes are often found in folk music, pop music and jazz.
When a piece of music changes key, it is said to modulate. It is most likely to modulate to a closely related key.
The keys most closely related to the tonic are the dominant, the subdominant or the relative minor or major keys.
The chords above the bass may change, but the bass note stays the same.
In the example, the pedal note is C, which you can see in the bass part.
“Ground bass” is the term used in Baroque music where a bass part is repeated throughout the piece. Whereas an ostinato pattern might be very short, a ground bass can last many bars before it is repeated.