Note: To understand this article you’ll need to be familiar with basic chord theory and the use of Roman numerals to notate chords. (This link can fill you in.)

I often find myself having to learn songs quickly. (Related article: How to learn a lot of songs fast.) Often I’ll end up scouring the internet or my various music books for a chart for a particular song. And sometimes I’ll notice that different charts will have different chords for the same song.

To be clear, I’m not talking about situation where a song is charted in different keys. For example, you may come across a chart for a song where the verse is written as:
| Cmaj7 | Ami  | F     | G7     |
You may then discover another chart written as:
| Emaj7 | C#mi | A | B7.

The second chart is simply modulating the song from the key of C major to E major. But the relationship of the chords to each other is the same. In numeral notation this progression would be written as I | vi | ii | V7.

Anyway, modulation is not what I’m referring to when I say the chords in two different charts are different from each other. I’m referring to a situation like the following:

One chart notates the first four bars of a song as:
| C     | F     | G     | C       |
And another chart notates the same bars as:
| C   C7   | F   Dmi | G7  G7#5 | C   G7  |

So how is this possible? Aren’t the chords of a song set in stone? If you change them around doesn’t it become a different song?

Well, not necessarily. You can alter the chords of a song and it will remain recognizable. You can also “jazz up” your own tunes by adding in new chords or altering the ones you have. However, it’s not simply a process of trying to blindly swap one chord for another. When looking at a particular chord you’ll find that some chords make better candidates for swapping or adding than others.

Let’s look at some common chord substitutions and alterations.

Add a diatonic 7th or other extensions to triads 

Let’s again look at that same progression  shown above:
| C     | F     | G     | C       |

These are some pretty basic and common chords in the key of C major. Play these chords and come up with a little simple melody that you can hum over those them. Now sing the same melody over the following.

| C maj7     | F maj7     | G7     | C maj7     |

The original melody still works, but the progression sounds a bit different, perhaps jazzier to your ear (though not everyone will think so.) All we’ve done is add the 7th interval of each chord, drawn from the C major scale.

The 7th interval is probably the most common interval to add to a triad. But you can also add any other extensions (as they are called) from correct scale: 9ths, 6ths, 11ths. Try your melody over…

| C maj9    | Fmaj#11    | G 13    | C maj9    |

Again, all these extensions are simply notes drawn from the C major scale. How’s it sound? It may be great, or may be not. Not every chord extension will support every melody.

Chord Substitution
This is the idea that one chord can be substituted for another. This is actually a complex topic that can be studied in depth. (If you want to do so, here’s a place to start.) I’ll just list some common substitutions here.

• iii and vi chords can be substituted for I chords (and vice versa.)
• ii chords can be substituted for IV chords (and vice versa.)
• vii half diminished chords can be substituted for V chords (and vice versa.)
• A common jazzy substitution is to replace a V7 chord with the dominant chord that is a tritone away. So, Bb 7 could be replaced with F7, or G7 could be replaced with Db7.

Let’s look again at our chord progression:
| C     | F     | G     | C       |

Let’s try out some of these ideas by substituting a new chord for the second half of each bar.
| C  Ami   | F  Dmi   | G  Dflat (C#)7   | C       |

In the first bar, we’re substituting the vi (Ami) for the I (C). In the second bar we’re substitution the ii (Dmi) for the IV (F). In the third bar we’re doing a tritone substitution.

Try humming your melody over this new progression. Again, results will vary depending on the notes of your melody but this can give you some interesting options to play with.

Chord tone alterations
There are several situations where altering a note in a chord can offer interesting results.

Playing with thirds
Let’s consider a situation where a IV chord is right before a I chord. You can lower that IV chord’s major third to a minor third and get a nice sound. For example, in the key of C you’d have something like:

| F  Fmi  | C    |
Or you could just replace the F with F minor from the get go.
| Fmi      | C     |
Obviously this won’t work well if the major third of F, the A note, is a prominent part of the melody.

Let’s consider a situation where a minor chord is preceding a chord a fourth above it. This could be the ii chord going to a V chord, or a iii chord going to a vi chord, or a vi chord going to a ii. In these cases you can change that minor chord to a major for pleasing results. For example, take a look at this iii vi ii V progression in the key of C:
| Emi   Ami   | Dmi   G7   |

We’ve got a iii going to vi (Emi to Ami), a vi going to ii (Ami going to ii), and a ii going to a V (Dmi to G7). All sorts of opportunities abound. Try out the following.

| Emi E Ami  | Dmi D  G7    |
Or…
| E    Ami    | D    G7     |
Or…
| Emi  Ami A | D   G7  |
Or even…
| E7  A7  | D7   G7| (This one is pretty common in early jazz.)

As you probably noticed, in that last one we’re doing more than just going from a minor to major, we are are also added in a dominant 7th interval. As a result, for example, Emi isn’t just becoming  E, it becomes E7. I just think this sounds better.

Raising the fifth
Consider a situation where a major chord is leading into a chord a fourth above it. A V chord going to a I chord is a perfect example, and one you see all the time. You can raise the 5th interval of the V chord by a half step. This turns the chord into what’s called an augmented chord (often denoted with a little plus sign, like G+.)  For example, in C…

| G7  G+7  | C    |

You could also apply the following transformation on a iii vi ii V progression (the progression we discussed in the “Playing with Thirds” section above.) We first raise all the minors to major so that
| Emi   Ami   | Dmi   G7   |
becomes…
| E7  A7  | D7   G7|
And then raise the fifth on all of them, leading to…
| E+7  A+7  | D+7   G+7|

It’s going to start getting pretty “out there” so you’ll probably want to use these ideas sparingly. But I want to give a sense of what’s possible.

Tweaking the 7th
Now let’s consider a situation where a I chord is going to a VI chord. We can add a dominant 7th to make that transition more prominent. So…
| C     | F     |
becomes…
| C   C7   | F     |
or just…
| C7     | F    |
You hear this sort of thing often in country tunes.

We could even do something interesting by first using the maj 7th, then the dominant 7th, like…

| Cmaj7 C7   | F      |
You might be familiar with some Beatles songs that do this.

Adding the V7 chord
Here’s a final trick to play with. You can “approach” chords with a dominant 7th chord built off the note a fifth above the root note of the chord. For example, consider an Ami chord. Its fifth is E. So you can precede the Ami chord in a progression with the E7 chord.

Consider this progression.
| C      | Ami     | Dmi     | G     |

Let’s add in an E7 before the Ami, like so:
| C   E7   | Ami     | Dmi     | G     |

But this works not just for the Ami chord, but any of these chords. Let’s add these dominant 7th chords in for all of the chords in the progression.

| C   E7   | Ami  A7   | Dmi  D7   | G  G7  |

It’s interesting to note that we end up with chords similar to when we raised the thirds in the “Playing with Thirds” section. In a way, this idea is just another way of looking at things. There are a lot of situations in music that can be “explained” by two or more different explanations.

Know your audience
Keep in mind that these ideas work better in some genres of music that others. In jazz and jazz pop its quite common to change things around, often on the fly. In rock and more conventional pop, swapping out chords may change the fundamental character of the song and people will complain. Different music audiences are more forgiving than others when it comes to alteration.

Simplify the complex
One more thing to keep in mind. All these ideas that make simple songs more complex can be used in reverse to to make complex songs simpler. Say you are presented with a progression like:
| C   C+7   | F    Fmi  | C      | C      |

That C+7 is probably just a case where the 5th was raised and the 7th lowered to lead into to the VI chord (the F.) And the Fmi is just the major third being lowered to lead back to the C. You could try simplifying it as such:

| C       | F      | C     | C     |

As with all of this, results vary. If it sounds weird it’s probably because the melody is in some way clashing with the new changes. But you will be surprised at how often you can tweak things with no problems.