In music, every key has something that we call the “harmonic field”. This is a concept which allows us to figure out which chords work and sound good when we are playing or composing music in a certain key.

The harmonic field is built by taking the notes that make up the scale of that key (for example, C Major scale for music in C Major) and harmonizing each degree (each note) by stacking thirds on each one, giving us the chords that exist in that key.

Maybe this sounds a bit overwhelming without any visual representation or practical examples, but once you understand it clearly, you can then figure this out for any key very easily, just by following a simple formula.

The key of C Major is the easiest to comprehend, due to the fact that it has no sharpened or flattened notes, which makes it the perfect key to understand how this concept works, so you can apply it to other keys later on.

Chords that belong to the key of C Major

Chord Diagrams

How to figure out what chords fit into a certain key

You now know which chords fit into the key of C Major, but we still haven’t seen how we would reach these chords from scratch, which is what we are going to go over now. The logic applied here works for every other key!

In order to build the harmonic field of a given key, you must start with its corresponding scale. In this case, we will work with the C Major scale as our starting point. 

The biggest advantage of using C Major to explain any type of musical concept is that it has no sharps or flats, all notes are natural. This is easy to comprehend if you’ve got a keyboard: the C Major scale goes from C to C using only white keys (black keys correspond to sharp and flat notes).

So, starting with the C Major scale, we have the following notes:

• C, D, E, F, G, A, B.

Start by writing these notes on a staff (you’ll see a demonstration of this below).

Next, we need to build triads on every degree (every note) of the scale.

You do this by stacking thirds on each one, until you’ve built a triad (three note chord). You will end up with the root, third and fifth of each triad.

Since C Major is made up of natural notes only, you don’t need to pay much attention, you can’t forget about a sharp or flat because there aren’t any! 

Stacking two third on top of each degree of the scale will get you something that looks like this:

As with any musical concept, it is always good to understand where everything comes from, instead of simply memorizing a formula that gets you where you need to go quickly and without a lot of mental gymnastics, and this topic is no different.

However, there’s a very easy way to figure out the quality (major, minor or diminished) of every chord within any key. 

There’s a pattern that you can observe every time. Here’s what you should definitely memorize as soon as you can:

• Degrees I, IV and V are MAJOR (root, major 3^rd, perfect 5^th)

• Degrees ii, iii and vi are MINOR (root, minor 3^rd, perfect 5^th)

• Degree vii is DIMINISHED (root, minor third, diminished 5^th) 

By memorizing the quality of each degree of the harmonic field, you can easily tell which chords you have available, regardless of the key you are playing or writing in, which saves you time and allows you to make quick decisions on the fly.

However, there is one detail that you must not forget about – every key has its sharps or flats (except for C Major and A minor). Take those into account, or your chords won’t be right!

For this, the is a great tool, as it shows you which notes are sharp or flat in each key.

Aside from the circle of fifths, another great way to keep track of which chords are sharp or flat in a given key is to always remember that major keys have a semitone interval between the degrees iii – IV and vii – I.

In C Major, this happens between Em – F, and Bdim – C.

In the event you’re working with a minor key, these intervals occur between degrees ii – iii and V – vii.

Once you have these particularities of the harmonic field interiorized, it will be difficult for you to make a mistake, as it will all become quite intuitive! It will come in very handy when you want to write a song and need to know which chords you have at your disposal.

This doesn’t mean that the seven chords within the harmonic field are your only choices. There are others, such as the ones that come from modal interchange, but that is a different topic.

Since the majority of songs are based on very similar chord progressions, knowing and understanding the harmonic field and tonal function of each degree is a very important skill for any musician and songwriter.

Check the next section to see some of the most common chord progressions you can find in the key of C Major.

Popular chord progressions in the key of C Major

Conclusion

In short, if you invest some time and memorize which degrees of the harmonic field are major, minor or diminished, you’ll save time, and you’re less likely to make a mistake over a small distraction. Knowing the accidentals (sharps or flats) of each key is crucial too.

After some time practicing and trying out several chord progressions, you will start to gain skills which will allow you to figure out songs by ear quicker, and also write more powerful chord progressions by yourself.

As you can see, there really aren’t any excuses not to master this concept!

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