How Do I Know What Chords Are In A Key?

By | May 7, 2018

We have discussed major scales and keys, and we have learned that chords come from these keys. We know about triads, which are the simple three-note chords which have names like “Major,” “minor” and “diminished.” In a previous lesson, we went through a fairly complicated step-by-step process of listing all the triads we could find in the key of C Major by starting on each note in the scale and then “skipping” a note in the scale, and then “skipping” again. We learned about chord-tones, too. And we learned how to tell which type of chord a triad is by measuring the distances between its notes. Yet, you may still be asking, “How do i know what chords are in a key?”

All of the information we discussed involving triads and their formulas was fairly mathematical and seems quite complex when it is new to a musician. Trust that with a little time devoted to thinking about it, it will start to seem more natural. What may come as a relief is the fact that you don’t need to go through all that thinking every time you want to know what chords are in a key!

Being able to figure out what chords are in a key, and conversely, what keys a chord belongs to are very important skills a musician must have in order to improvise intelligently. In fact, this information pretty much solves the mystery of how to improvise and can also be very useful for songwriting.

Let’s remember that all keys are similar with regard to the distances between their notes. Every key begins with a note (the root of the key) and proceeds through the following progression of intervals before coming back to the next root an octave higher:

whole-step, whole-step, half-step, whole-step, whole-step, whole-step, half-step

Musicians often assign numbers to the scale tones as a way to discuss the given scale without having to say specifically what key they are talking about. It’s a generic way to discuss it. For example a major scale contains seven notes. We could assign the numbers one through seven to the notes, allowing us to talk about major scales in general and not a particular major scale.

In the above diagram we use the letters “w” and “h” to represent whole-steps and half-steps, and the arabic numerals one through seven to represent scale degrees of a major scale. This is common practice for musicians.

In a previous post we listed and named all of the triads in the key of C Major. We found that the key contained the following chords: C Major, D minor, E minor, F Major, G Major, A minor and B diminished.

Here is the beauty of this – since all keys are exactly similar with respect to the distances between their notes, then all keys will have exactly the same types of chords, in exactly the same order! The order is always Major, minor, minor, Major, Major, minor, diminished. Only the names of the roots will change. For example, the key of D Major contains the following notes: D-E-F#-G-A-B-C#. Applying our new knowledge about the order of the chord-types, we know all the chords in the key of D Major:

D Major, E minor, F# minor, G Major, A Major, B minor, C# diminished

Or in the key of B:

B Major, C# minor, D# minor, E Major, F# Major, G# minor, A# diminished

Makes life a bit easier, huh?

Let’s talk about one last thing. . .

Not only do musicians use numbers when discussing the notes in a scale, we also use numbers when discussing the chords in a key. But when we are referring to chords we use roman numerals instead of the arabic variety. Why? So we can capitalize the Major chords, and use lower case numerals for the minor chords. As you can see in the example below, we use lowercase numerals to represent the diminished chord and we give it a small superscript circle to differentiate it from a minor chord.

Using roman numerals to represent the chords in a key is also standard practice among musicians.

This allows me to say things like, “The ii chord in the key of D is E minor.” Or, “The IV chord in the key of B is E Major.” So, if you don’t know your roman numerals up to seven, you should definitely learn them. A simple Google search will do it, I’m sure.

I am going to post a reference sheet shortly which will have all the keys written out as well as their chords. In the meantime this is a great place in our studies to pause and spend a little time making sure we understand everything so far. If there are any questions, leave them at the bottom of the page in the comments form. I will make sure they get answered.

Take a little time to catch your breath and give yourself a pat on the back. We are going to start talking about improvisation soon. And seventh chords.


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