As I-IV-V is so prevalent, I can usually pick that out in a song, unless the order gets reversed. I-IV is pretty easy to distinguish - I-V for some reason is harder for my ear to pick up. Any more complicated than that and I have to use the method of humming along with the mystery chord. I can usually pick out the root note. Then I stop the music and match the hum to the root note on the guitar. If it's a major, minor, major or dominant seventh, or occasionally a ninth I'm home free, as these are the variations with which I am most familiar. The complicated ones (the ones WyoWoman refers to as having everything including the kitchen sink thrown in)...it's time to get out the toys. Record the chord in question, freeze its occurrence, and move my fingers around until I match the chord note for note. Then, for me it's important to give it a name other than "that weird #4%^ chord." I go to a chord finder program, punch in the notes and see what the program comes up with. I'm not particularly concerned if the name follows standard protocol - I just want something to call it.

My unorthodox method for discovering the "lost" chords.

Neil