3rd Intervals | A Simple concept for pro sounding melodies

Someone recently asked me: "I'll often play chords under my melodies but what can I do when I have a series of melody notes that last for one or more measures?"

This is a great question because I get it often and there's more than just one answer. If you're including the melody of the song in your arrangement, (aka solo piano) it's very common to spread out the chord voicing in both hands. And as per the question, you may have a series of melody notes that last through one or more measures.

It's common for a musician to not want to play them as single melody notes. Even though you may have the option to play a 6th interval under the melody, the opposite of that would be to play a 3rd interval under the melody.

Let me explain.

As you may know, an interval is the distance between notes. A 3rd interval is two notes that are three notes from each other (inclusively) in the key you're playing in.

Let's look at 3rds in the key of C Major

In any key of music, notes that are a 3rd interval apart are separated by one note that's in the key. However, the most common way to execute a 3rd is simply to count from the starting note to the 3rd note inclusively.

As you can see, it's quite easy to find the 3rd of any note in the key. However, if you're playing a melody, the 3rd needs to be under the melody. So, instead of counting up three notes from the melody note, count three notes down from the melody note.  The following illustrations show how the first tone could be harmonized with 3rds in various keys.

An excellent way to rehearse harmonizing a melody with 3rds is to play them up and down a key. Because there aren't any black keys in the key of C Major, it's the easiest key to study your 3rd intervals in.  The following illustrates every melody note in the key of C Major harmonized with a 3rd.

So what would be a good example of using 3rds in an actual piece of music?

Let's take the following excerpt from a lead sheet that has a succession of melody notes in the key of C Major.With this melody scenario, harmonizing it in 3rds would look like this: