For every key there is, there is something called the “harmonic field”. This is nothing more than the set of chords that fit into that key. These can be built upon each degree (each individual note) of that tonality by stacking thirds on top of each one.

As every tonality has its own set of accidentals (notes that are either sharpened or flattened), the chords that are formed by stacking thirds on each degree will naturally be distinct too.

Although this may seem like a tricky topic at first, it really just follows the same formula for every single case, so once you become familiarized with the way it works, you’ll be able to figure out the chords for any key with quickly and easily!

Chords that belong to the key of A Major

Chord Diagrams:

How to figure out what chords fit into a certain key

Now that you know which chords exist within A Major, let’s check how you could figure them out on your own. The rationale shown here can be applied to any other key!

Before you build this “harmonic field” for any given tonality, you must first know if its scale has any sharps of flats. , for example, hasn’t got any, but A Major is different. 

In order to know which chords fit into A Major, we need to start by writing the A Major scale.

If you check the circle of fifths, you’ll see that the A Major scale has the following notes:

• A, B, C#, D, E, F#, G#.

Now, in order to go from the individual notes of the scale to the harmonic field, you need to build triads for every degree of the scale.

This is done by stacking thirds on each degree until you have three notes, which will be the root, third and fifth. 

The sharps or flats of each note on any given scale will determine which triads end up being major, minor or diminished.

Taking this into account, if you lay out each note of the A Major scale on the staff and start stacking thirds on each one while respecting the fact that C, F and G are raised by a semitone, you get this:

While it is always a great idea to make an effort to understand the logic and theory behind something such as a harmonic field, there is a way to deduce the quality (major, minor or diminished) of every chord within any key.

Regardless of the key you’re working with, there is a pattern that always repeats itself. The following will always be true:

• 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) 

If you memorize this, you can deduce which chords fit into any key much faster than if you had to calculate and write the triads that are built upon each of the scale’s degrees. 

The one thing you must pay close attention to are the accidentals (sharps or flats of that key), as a mistake there will yield a harmonic field that won’t make sense. 

Once again, the is your friend!

Circle Of Fifths

Another detail that will help you build any harmonic field without making a mistake is knowing that if you’re working with a major key, you will always have a semitone interval between the degrees iii – IV and vii – I. 

If you look closely at A Major, you’ll see that you have a semitone between C# minor – D major, and also between G# diminished – A Major. 

In case you’re working with a minor key, you’ll also have these semitone intervals, but instead, they will appear between degrees ii – iii and V – vii. 

Remembering these tips will make sure you never make a mistake while building the harmonic field of any key! This will be most useful when you want to write a song and need to know what chords you have at your disposal.

Obviously, there are more chords that will work within a key, such as the ones that come from modal interchange, but that is a different story.

Understanding the chords in the harmonic field and their respective tonal functions is a fundamental skill for any songwriter, since most songs are based on the same (or very similar) chord progressions.

You’ll find a few of the most common and popular chord progressions within the key of A Major in the next section.

Popular chord progressions in the key of A Major

Music is all about creating tension and resolving it, and this effect can be obtained by combining chords that have different tonal functions within the key they belong to. 

If you take the chords from a key such as A Major and assign numbers to each degree (I, ii, iii, IV, etc.), you can easily talk about the chords you want to use, and the biggest advantage is that you can quickly transpose that progression to a different key. 

The chords will have different names in other keys, but the relationship between them is the same, which is why it is easier to use roman numerals when discussing harmony like this.

Here are a few progressions you can try out for yourself, and maybe try to come up with a melody that works well with them!

Conclusion

In summary, if you memorize which degrees of the harmonic field are major, minor or diminished, you’re much less likely to make mistakes. Knowing which degrees are sharpened or flattened in each key is also fundamental.

By practicing and experimenting with various chord progressions, you’ll be able to figure out songs by ear better in the future. Composing new music will also feel more intuitive, as the function of each chord in the harmonic field becomes clearer to you!

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