Tonic-I Chord

When I hear a chord progression, I think of the chords as going from one "place" to another. The usual destination of all this movement is home. Home is the I chord also known as the tonic. The roman numeral is used to indicate that this chord is based on the first scale degree of the key, so in the key of C major, this would be a C. The entire chord would be built up in diatonic(in the key) thirds(root-3rd-5th) from the root note C, so the full chord is spelled C-E-G. This always sounds to me like it is a place of rest or a place where everything is resolved. Some of my students hear these chord progressions and chords as colors or as a "feeling". How you describe them doesn't matter to much as long as you hear a movement.

Dominant-V or V7

As the chords go from one to another, you are hearing something that progresses from one place to another (or from one "color" to another). One of the other prime chords is the dominant or V chord.(G chord in the key of C).  It is based on the 5th scale degree. This one sounds to me like it wants to move somewhere, especially if we include the lowered 7th of the chord. This additional 7th sets up an unstable interval that occurs between the major 3rd and the lowered 7th and has a strong tendency to move. When it does, it is said to have resolved. Often, the dominant chord will resolve to the I chord. It doesn't have to resolve to only the I chord. It can also resolve to any other chord.

Subdominant-IV or II-7

Another chord that wants to move but not as strongly as the V7 is the subdominant or IV. This chord is based on the 4th scale degree(F in the key of C major). It is sometimes easy to confuse this with the tonic as they are both major chords and if we include the 7th there is no unstable interva that existl from the 3rd & 7th.  This chord can resolve either to the V chord or the I chord. When you hear the IV chord resolve to the I chord you are hearing the cadence from church "A-men".

Common Chord Progression-II-7/V7/I

A very common progression that you will hear is subdominant to dominant to tonic or IV-V7-I. Many times, jazz musicians like to use the II-7 (the - means minor). This chord can be used for the subdominant as it contains 3 of the same tones as the IV chord and therefore, can function the same as the IV chords; that is, as a subdominant. It is based on the 2nd scale degree (D in the key of C) If you can hear this movement between chords and be able to detect what chord is moving, you will be able to appreciate and enjoy the music more. If you are serious, you may want to consider attending an ear training class or private instruction.