A song without a 'chord progression' is a song with only one chord. A chord progression refers to a series of chords that lead from one to another. Songs usually consist of one or more chord progressions that are repeated throughout the song. Many songs have several chord progression patterns - One pattern or progression for the verses, one for the bridge (if a bridge is included), and one for the chorus or refrain. Some songs use one chord progression throughout, and simply change the melody or the rhythm and timing of the chord changes to give the song more dynamics and create more than one mood or "feel" from one series of chords.
In the western world, our music uses only 12 notes, and each of those notes can be accompanied by dozens of chords. You can play the chord that matches a note (e.g. sing an A note and play an A chord), or you can harmonize with a note, or series of notes, by using a particular chord progression to produce musical "colors". However, there is a finite number of chords, and a finite number of combinations in which they can be used together. Perhaps that is why there are countless songs that use similar chord progressions. By saying "similar chord progressions" I mean that the relationships between the chords are the same in many songs.
I should make this very clear before proceeding: When we refer to a "4th chord" or a "5th chord", we are not talking about the chronology of when a chord is played or its' order in a progression. In this context 4ths, 5ths 6ths' etc., refer to the scale position (interval) of a chord as related to a root, or starting chord.
Two songs can be in different keys and have the same relative chord progression. If you transpose the key of one song to the other you get the same relative chord changes or progression. Let me explain that further by giving an example:
You have probably heard the songs 'Louie Louie' (by the Kingsmen), and 'Wild Thing' (by The Troggs or the Jimi Hendrix version). Let's say that 'Louie Louie' is in the key of A, and 'Wild Thing' is in the key of E. The chord progression for 'Louie Louie' (regardless of how you strum the chords) is: A, D, E, D. In music terms we would say you start with the root chord (A), move up a 4th (D), move up to the 5th (E), then back to the 4th (D), then repeat from the beginning. The chord progression for 'Wild Thing' (regardless of the strumming) is E, A, B, A. Again, in music terms you would say: You start with the root chord (E), move up a 4th (A), move up to the 5th (B), back to the 4th (A), then repeat from the beginning. Notice that in both cases we started with the root chord, moved up to a 4th, then up to the 5th, then back to the 4th. Therefore, the relationship between the chords is identical for both songs. We could play both of those songs in ANY key we like, as long as we keep the order and relationship between the root chord and the subsequent chords the same.
Figure 15-1 is a table showing all Major scales. Notice that each column of the chart shows a series of notes 1 semitone (one fret) apart. That indicates the relationship between the root of any scale or chord and the number of steps or semitones between the root and any interval (the 2nd, 3rd, 4th, 5th, 6th, Dominant 7th, and Major 7th) are the same for all root notes and chords. By keeping that in mind, and using the chart, you can transpose the chords of songs in any key to any other key. Read the lesson SCALES for more information about intervals (3rds, 4ths, 5ths, 6ths, 7ths etc.)
When changing from one chord to another we will use the numbered intervals of the scales in relation to the root chord of the progression. If a chord progression begins with an F and moves to a "5th", we could look at the chart to see that the 5th in the Major scale of F is a C. Using this method allows us to choose any 'Root' chord, or key signature, and show the progression without needing to name the root chord or the key signature of the song. That makes it easy for us to transpose the chord progression to any key.
We saw how the songs "Louie Louie" and "Wild Thing" used the same relative chord progression in different key signatures, despite having different rhythms and timing. "Louie Louie" was played in A, progressed to D and E and then back to D. "Wild Thing" was played in E, progressed to A, then to B, and then back to A. Look at Figure 15-1 to find what the chord progression would be if you played those songs in C (hint: use the same relationship between the root, 4th and 5th). The answer would be C, F, G, F because C is the root, F is the 4th of C, and G is the 5th of C.
You will find that many songs, in all genres, use progressions that involve the root, the 4th, and/or the 5th - in a variety of combinations and at various times. Figure 15-2 shows a few examples of some common chord progressions using those three relative chords. All examples are in 4/4 time (4 beats to each bar). The numbers shown above each chord element represent the beats per chord.
Often, a DOMINANT 7th is added to the 5th chord. To find a Dominant 7th of the 5th chord use Figure 15-1, find the 5th chord from the root and then find the dominant 7th of that 5th. For example: If the root is C the 5th is G and the dominant 7th of G is F, so, a G7 chord is a G with an F added.