In music theory, you’ll commonly see chords referred to as their Roman numeral. This makes it easy for us to use the same concepts in different keys. For example, a I chord in C major is C major. But a I chord in D major is D major. To take that a step further, a V chord in C major is G major, whereas a V chord in D major is A major. Shifting the same relative pitches from one key to another is called “transposition.”
All of these types of chords are used in rock music. But there is also another, simpler type of chord used in rock chord progressions. It is called a “power chord.”
Power chords are similar to triads, but they only consist of two notes – the root, or first degree, as well as the fifth. We can make a power chord out of any triad by removing the third degree of that chord. If we take a C major (C, E, G) and remove the E – which is the third – we are left with a C power chord. Power chords are also sometimes referred to as “5” chords, like “C5”.
To hear the difference between a triad and a power chord, let’s listen to them side by side. Here is a C major chord: