An example from the blues song Chilly Winds:

C F C C⁷ F⁷ Db⁷ C G⁷ C

Usually this will be presented above a single line of music. The single line will be the sung, or vocal line--call it the melody.

There will be no left hand, or any instrument part. The changes are to facilitate the artist's musical imagination--to create the comping in the given chord progression, but with complete freedom to improvise and plan a two-handed harmony and rhythm. (I'm thinking of a piano or keyboard.)

The vocalist--if accompanying another--will not want someone stealing his or her melody. And if accompanying onself, one doesn't want something so complicated that it takes up too much attention.

Try singing and playing all by yourself! It's fun, but takes more than a little concentration.

Short story written by Neil Gaiman (Sandman, Neverwhere, American Gods) and included in Smoke and Mirrors, a collection of short stories and prose by said author.

Synopsis

The general premise of the story goes something like this - what would happen if a cure for cancer was discovered? Sounds like a simple enough question to answer and the general reaction would probably be "Hell, yeah, that would be the best!"

However, the story deals with the overwhelming effects the cure has on human evolution as it does exact a terrible price with its side effect.

It's at this point that I will warn you not to read any further as there are...

MAJOR SPOILERS AHEAD!

3

2

1

Our protagonist, Rajit, has developed a new drug that defeats cancerous cells by essentially repogramming the genetic code within the human host. The result is a cancer-free body but the side effect is that the body also becomes "gender-reprogrammed"...meaning a male patient would become a female or vice-versa, with all of the genitalia and added body parts to match. The gender switch would only last as long as the drug is in effect but is required for the cancer to stay dormant.

While the drug (dubbed Reboot) is widely hailed as a breakthrough in modern medicine and its creator called a hero, the discovery of the side effects also provides trouble for Rajit as he is labelled a pariah by religious and right-wing groups.

That doesn't even begin to tell you the widespread mayhem the drug causes in humankind. For example, the story also covers the following:

• Even though the drug is approved and regulated by the FDA, there is a healthy black market for its recreational use...it seems that plenty of people enjoy its ability to gender swap (dubbed changing) and do so in record numbers.
• Families in China, still under the one child rule, use the drug to change their newborn daughters into boys. The population begins to dwindle as a result of less females so the government sanctions the use of the drug to reverse the changes.
• A new business of being able to truly identify the gender of a person becomes a prosperous one. The ability is limited only to a few thousand people.
• A movie about Rajit's discovery is made (Reboot, directed by Robert Zemeckis and starring Jeff Goldblum). The story exaggerates so many things, including Rajit's sexual preference (the movie's Rajit has a beautiful blonde woman at his side...the reality is much different).
• As a result of its use in describing the side effects of Reboot, the word change becomes a profane word. Wait till you see what they come up with as replacement words to describe loose coins and putting on different clothing!

The above only scratches the surface in this story (which covers the span of about 7 decades) but you will have to read it to find out more.

Conclusion

A very spooky fable about the dangers of letting science overwhelm human nature and judgement. Gaiman dissects the story into little chapters, each of which cover a result of the drug around the world and with individuals. Highly recommended.