Question: What can I do to be able to identify all the chords in a song that I want to play? For example, let's say I have a guest singer coming into my band to sing a very hard song that he brought on a CD. I have never heard this song before, and the singer does not know anything about music beside singing. What is the best way for me to figure out the chords of the song that he wants to sing on the spot and start rehearsing right away? How can I get better at doing this easily without taking the whole rehearsal time to figure out just one song? Is it maybe because I have never learned how to play a single song? Of course, there are easy songs that are more simple to figure out, like the ones built on a I IV V progression, but I am talking about hard songs with more complex chords and perhaps key changes. What can I do to solve this problem?
Tom Hess's Answer: To learn how to identify chords in a song, you need to start working on your aural skills (training your ears) AND you need to learn music theory concepts that will help you to understand exactly what it is you are hearing. Ear training and music theory need to complement each other so that you can instantly (or almost instantly) identify what the chords are in any chord progression that you hear. This is what you need to master in order to reach your goal.
When you learn a music theory concept, make sure that you also learn what it sounds like when played in a musical context (it's not enough to simply "understand it"). Likewise, as you learn how to play guitar by ear, make sure that you understand how the musical phrases you are hearing work in music theory terms. For example, once you learn what a i VI ii V i progression sounds like (using your ears) and you understand how and why it works in music theory, you will be able to identify it in every song it occurs (no matter what the specific musical context is).
When master musicians transcribe unfamiliar songs or learn new music on the spot, they are relying on these two skills (knowing how to play guitar by ear and knowledge of music theory) developed to a very high level. Most guitar players make the mistake of either not studying music theory and aural skills at all, or only studying one of these areas in isolation. As a result, they never become the awesome musicians they could be.
Although it may seem hard to believe that it is possible to learn to develop guitar ear training to where you can hear a song and learn it by ear very quickly, this skill is attainable by anyone. I have learned this to be true after teaching hundreds of students to develop this ability.
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