Imagine that you are the main pianist for your church. One day an evangelist comes to your church and you have to play “Amazing Grace” for his wife, who is going to sing a solo that night. Unfortunately, she wants you to play it in the key of Ab and your church always sings it in F. You have thirty minutes before church starts! What do you do?
Ok, true, you could cheat and use the modulation function on your keyboard, but let’s imagine that you keyboard doesn’t have one of those. What now?
Let me just tell you, the time will come when you will need to know how to transpose a song into a different key. Here is how you do it. Let’s take “Amazing Grace” as an example. Here it is.
The first thing we want to do is rewrite the song using Roman Numerals.
For example, “F” is the I chord. So in place of “F2” we write I2. “C” is the V chord, so in place of Cm9, we write v9.
(Remember, lower case Roman numerals signify minor chords.)
Now, we can transpose the song into any key we want.
Now let’s transpose it to Ab doing the same thing. In place of I2, we write Ab2, and in place of v9, we write Ebm9. (Or you can just line the scales up and replace each note.)