If you want to compose music chords are of the essence. They are the inner soul of music! But before we we are going to play with them, first we have to tell you a thing or two about music note names, chord names and their notation.
Notes I to VIII
Each note of the scale is considered a scale degree, and Roman numerals (I, II, …) are used to identify them. The notes also have a name to describe their relationship to the other notes in the scale and to the first note, the key note or tonic. These names are, in ascending order: tonic, supertonic, mediant, subdominant, dominant, submediant, leading note and octave (which is of course the tonic one octave higher). In the next picture the notes of C major are shown, with their degrees and note names.
Chords I to VII
Traditionally the Roman numerals (I,II,..) also were used to identify chords, but in modern music symbols (C,Dm,..) are used . We will use both, because with the Roman numerals the function of the chord in relation to the tonic and to the other notes is visible (we will learn much more about function later), and modern symbols are nice, simple and easy to grasp (though the function is not clear anymore). Together they tell you all you need to know about the chord progression(s) we are going to study. The next picture shows all seven triads of C major with Roman numerals and modern chord symbols
Notice that the numeral VIII is not used to identify the last triad. There are eight notes, but only seven chords. Why is this? The last chord is of course the same as chord I, one octave higher.