To begin with, you should already know the basic chords, and how to tune your guitar. Make sure you listen to a lot of guitar music. Pick a recording with clear guitar sound to learn how to play guitar by ear.
Tune your guitar using a tuner, pitch pipes, or harmonica. Most recordings will have the guitar in standard tuning: E, A, D, G, B, E, from the largest to smallest string. However, some guitar recordings, such as Stevie Ray Vaughan or AD/DC, will have all the strings tuned down one note. In such cases, you can find the lowest note on your guitar that is close to the first bass note in the recording. Then, tune that string so that the note on your guitar is the lowest note in one of the basic guitar chords. Then, tune the guitar with that string as a reference.
The next step is to find your key. That first note of the bass in the recording is the root note. The key of the song has the same name as that note. Play the major and a minor chord. Whichever one sounds like it fits, is the 1st or tonic chord of the song.
Next, find the 5th chord. This is the dominant chord. Count 5 notes from the tonic chord, in the series ABCDEFG. When you hit G, loop back to A and keep counting. As an example, if your tonic chord was E major, then the fifth note you count should be B. The dominant chord is always major, so B major is the 5th chord.
Now, find the 4th chord in the same way. If the root was minor, the 4th will be minor. If the root was major, the 4th will be major. This is called the subdominant chord.
Always remember, that everything in a song centers around the most important tonic chord. An important part of Western tonal music is the movement from the 5th to the 1st chord. It often appears at the end of verses or choruses, and almost always at the end of a song. The 5th is often played as a 7 chord, such as D7 in the key of G major.
Whatever happens before this movement from 5 to 1 depends on the song. The most basic pattern is 1-4-5-1. Rock and country songs will usually have a variant of this pattern, such as 1-4-1-5-1. Jazz songs usually have some variation on a theme of 2-5-1. In a major key the 2nd chord, the supertonic, is minor.
The 6th chord, or submediant, is often important in rock and pop. After the other 1st, 4th, and 5th chords have been added, the 6th adds variety anywhere in the song. It is often the first chord in the bridge of the song.
As you learn different songs, you will start to see different patterns and variations of these. You will also notice that artists have favorite patterns they use over and over. This makes it easy to learn more of their songs, because you know what to expect.
This process is fun right away. Over months and years you will become more of an expert. Soon, you’ll find you can quickly learn just about any song you want to by ear.
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