Harmony is the language of musical relationships. When you feel a yearning in music, that is the harmony, when you hear a build of tension in music, that is the harmony, and when you feel a finality at the end of the piece, that is harmony too. And the most basic building blocks of western classical harmony are I and V.
Let’s start from the beginning.
A major or minor scale is made up of eight notes. Each of those notes is assigned a number depending on the scale degree. The first note is I the second note is II the third is III and the fourth is IV and so on it goes up to VII. There is usually not much point in using VIII because it is the same pitch as I. You may wonder why we are using roman numerals instead of numbers, well the best reason I can think of is clarity. There are already plenty of numbers flying around on a score, so roman numerals are reserved only for harmony, and also fret numbers on the guitar.
Here is a C major scale with roman numerals just to make things clear:
Each of those scale degrees can be harmonized, creating a chord and these harmonies retain the same roman numeral. For instance, if the first scale degree in C Major was harmonized, it would make a major chord (C Major) and would be assigned the roman numeral I. If the note G was harmonized in that scale it would form a G major chord and be given the roman numeral V.
So, when I say play I and V in C major, you would play a C major chord and a G major chord. The same idea applies to the other scale degrees, some create a minor chord some a major, and the seventh creates a harmony that is different again. What is important for you to understand is that when I say I and V I am talking about harmonies in a key.
Just to hammer home the point, the scale of G major is:
G A B C D E F# G
So the first scale degree is G, and the fifth scale degree is D.
So, if I asked you to play I and V in the key of G major you would play, G Major and D Major.
V is always going to be major, which is handy to know. I will be major in a major key, and minor in a minor key.
Therefore, in the key of A minor the i will be A minor and the V will be E Major. You may have noticed I just used a lower case i there instead of an upper case. This denotes a minor harmony.
Why are I and V important?
I and V make up the most fundamental harmonic relationship in western classical music. It is like the ying and the yang. Tension and stability.
The good news is that you already are very familiar with I and V, they permeate all music, be it pop rock jazz classical or blues. Just think of the end of a Beethoven symphony and you will hear I V I V I V I V I over and over again. Have a go playing those chords quickly on your guitar and you will see what I mean.
How is this going to help me?
Well, I am glad you asked.
Once you become aware of the I V relationship, you are going to start seeing it pop up all over the place, and this will make music sound and look different. You will start to see connections and groupings that you couldn’t see before. This will help your reading, memorization, interpretation and general musicality, Suddenly those notes on the page wont seem so random all of a sudden…