What is a chord?
A chord is a collection of notes played simultaneously. There are many different types of chords, but for this task we will just be looking at triads. A triad is a collection of three notes stacked in thirds. When we are trying to find what triads to use in our scale, we can simply go up the scale, adding a third and then another third for each note to find the chord.
Scottish Reels usually only make use of around 4 chords: the I, IV, V and vi chords. Chords are written using Roman Numerals and take their names from the scale degree they are constructed from. So for the I chord, we construct the chord from the 1st note of the scale, which for example would be C in C major. We use a capital 'I' for the I chord since it is major. Similarly, the vi chord is constructed off the 6th note of the scale (A in C major), and the lower case tells us it is minor.