Do you feel stressed out when you hear the words “music theory?” Take a deep breath, remember that the circle of fifths has never killed anyone, and read on to learn how to make music theory feel less stressful and—dare I say it—fun. I’m going to tell you exactly what you need to know, why, and how you can learn it.
Before we jump in, remember that you’re not behind. Whatever level of knowledge you have is okay.
Start with the basics. Music theory is built of simple concepts. Even when you get into more complex theory concepts, they all come back to those basic building blocks. But if you jump into advanced concepts without knowing the basics, it can feel overwhelming. Give yourself permission to start at Square 1.
If you just thought, “That’s great, but I don’t even know where Square 1 IS,” I’ve got you covered. Here’s a basic outline of the things you need to know about music theory as a fiddler, plus why you need to know them and how you can learn them. I’ve given a little crash course under each header, but if reading these abbreviated explanations feels like too much too fast, don’t sweat it. I’ve noted the places in Fiddle School where you can go for in-depth learning and review on these music theory topics.
How to play a major scale.
You probably already know how to do this, so grab your instrument. Start on your A string and play an A major scale. Great! Notice two things:
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- Some notes are farther apart than others. A to B is a big step, while C# to D is a smaller step. These spaces between notes are called whole steps and half steps.
- There are seven notes in the scale. Keep this in mind for our next point.
Why you need to know those things: Whole steps and half steps are the building blocks of scales. Scales are the building blocks for all fiddle tunes.
Where you can learn or review these things in Fiddle School: You can review major scales throughout Session 1. Learn about whole steps, half steps, and how to build a major scale in Lesson 11.
How to think of notes as numbers.
Remember that A major scale? Play it again, and this time, assign every note in the scale a number. A is 1, B is 2, C# is 3, and so forth, until you get back to A (that’s 1 again). These numbers are called scale degrees. You’ll count seven scale degrees before you get back to A (1).
Unlike note names, scale degrees are not fixed. The numbers apply to different notes in different keys. For example, play a D major scale. Since you’re in the key of D now, D is 1, E is 2, and so forth. Want to play a G scale? Now G is 1. Et cetera. They key you’re in is always the first scale degree.
Why you need to know this: Unlike note names, numbers can be moved (like how A is 1 in the key of A and D is 1 in the key of D). That means that thinking of numbers allows you to find the notes you’re looking for in any key as long as you know the scale degrees you’re looking for.
Where you can learn or review these things in Fiddle School: Lesson 11, Lesson 15.
Key signatures.
In the last point, I mentioned keys. What determines what key something is in? Sharps, flats, and naturals (keep reading—we’ll get there). 
Go back to the idea of half steps and whole steps. In any major scale, there’s either a half step or a whole step (a small space or a big space) between one note and the next. The pattern of spaces is always the same: whole, whole, half, whole, whole, whole, half.
In the key of C major, your scale starts on the note C and the notes that follow are all natural (C—D—E-F—G—A—B-C). This creates the whole, whole, half, whole, whole, whole, half step pattern we just talked about. To create that same spacing pattern in other keys, we use sharps (these move a note up in pitch by a half step) or flats (these move a note down in pitch by a half step).
The key of G has 1 sharp, F#. The key of D has two sharps, F# and C#. The key of A has three sharps, F#, C#, and G#. You can learn and memorize the number or sharps or flats in each key.
Why you need to know these things: Understanding the spaces between notes and knowing the sharps or flats of a key allows you to build a scale in any key. It helps you know what notes you’ll play and what notes you’ll tend not to play in tunes within a certain key. It also allows you to take special notice when a tune includes accidentals (sharps and flats not within the key).
Where you can learn or review these things in Fiddle School: Lesson 11.
How to build arpeggios. 
An arpeggio is a few specific notes played one after the other. Played simultaneously, these notes would make a chord (we’ll get there in a second).
Again, go back to your A major scale. Remember the scale degrees: A is 1, B is 2, etc. Major arpeggios are made up of the 1st, 3rd, and 5th scale degrees. That makes the notes of our A major arpeggio A (1), C# (3), and E (5). Now try it in D. Use the same scale degrees: 1, 3, and 5. Your D arpeggio is D, F#, and A. Try finding your G arpeggio next.
Why you need to know this: So many songs are built from arpeggios. When you understand what goes into an arpeggio, you’re preparing yourself to grasp the structure of fiddle tunes and phrases. You’re also preparing yourself for improvisation down the road.
Where you can learn and review these things in Fiddle School: Lesson 15.
How to build chords.
A chord is made out of the same notes as an arpeggio. Again, that’s the 1st, 3rd, and 5th notes of the scale. The only difference is that all the notes are played simultaneously.
If you’re building an A major chord, you’re pulling the 1, 3, and 5 from an A major scale. Building a D minor chord? Pull the 1, 3, and 5 from a D minor scale. Building a G chord? You guessed it: pull the 1, 3, and 5 from the G scale and play those notes together.
Why you need to know this: When you understand the notes that go into a chord, you understand how what you play in the melody fits over them. This also prepares you for improvisation later and gives you the information you need to play fills or chords in a band or jam setting.
Where you can learn and review these things in Fiddle School: Lesson 11, Lesson 15.
How chord progressions work.
We’ve talked about everything up to how to build an individual chord. But what do you do with that chord? In a song, that chord is one chord out of a sequence of chords called a chord progression. Chord progressions are denoted measure by measure via chord charts. A chord chart might look something like this:
A D A E
A D E A
That’s a chord progression written out using the names of the chords. But in the same way we looked at an A major scale using numbers instead of note names, you can look at chords using numbers. Again, A is 1, but instead of talking about single notes this time, we’re talking about chords (built from the notes we talked about in the last point). Using numbers instead of chord names, the same chord chart would look like this:
1 4 1 5
1 4 5 1
A is your 1 chord, D is your 4 chord, and E is your 5 chord. Remember that scale degrees and chord numbers serve different purposes. I think of scale degrees as the trees and chord progressions as the forest. The 1st, 3rd, and 5th scale degrees (trees) make up each chord (grove of trees). Together, the chords make up the chord progression (the whole forest).
Why you need to know this: This is probably the most useful piece of music theory for you to understand as a fiddler. It’s part of everything you’ll do on your instrument, from playing fiddle tunes to improvising solos to playing chords and fills behind other musicians. You need to know the chord progressions of your songs to communicate with other musicians playing with you too. And since many fiddlers also play backup instruments, this is something you’ll need to know if you want to be an accompanist yourself.
Where you can learn and review these things in Fiddle School: Lesson 11, Lesson 15, Lesson 31, and throughout Fiddle School. You can also take a look at the chord charts within Fiddle School and practice rewriting them in numbers.
How the circle of fifths works.
The circle of fifths looks like this:
Start at the top with the key of C. Notice, as mentioned before, the key of C has no sharps and no flats. Now count C as 1 and count up to 5: C-D-E-F-G. Now we’re in the key of G. G has one sharp, F# (the new sharp will always be the last note in the scale). Now G is 1. Count up to 5. That’s D. D has two sharps, F# (keeping the sharp we had in the last key) and C# (the last note in the D scale). Counting up by five (or a fifth, thus the “circle of fifths,”) we reach A. A has three sharps, the two sharps from the last key plus a new sharp, G# (the last note in the A scale).
Seeing the pattern? We move a fifth to the right, we add a sharp. This works all the way around the right side of the circle, until you get to the key of F#. At that point we’ve got a whole slew of sharps (six of them), and that’s a lot to keep track of. Instead of adding sharps all the way around the circle, we add flats on the other side to keep things nice and neat. That way, we only ever have six sharps or flats maximum in any key. Let’s try out the left side of the circle. Start at C, where you have no flats. Now count C as 1 and count up to 4 (when we move counter-clockwise in the circle instead of clockwise, it becomes the circle of fourths). We arrive at F. The key of F has 1 flat, Bb. Counting up 4 from F as we move to the left in the circle, we arrive at the key of Bb. Bb has two flats, Bb, and Eb (the new flat will always be the fourth scale degree of whatever key you are in). The pattern continues as you move counter-clockwise.
“Okay, sure,” you say. “But couldn’t I just look up the key signatures and call it a day without getting into all of this?” Yes you could, I suppose. But there’s something else about the circle of fifths that makes it really useful for fiddlers: it gives you a visual of the most common chords used in fiddle tune chord progressions, the 1, 4, and 5 chords. Remember our earlier point about seeing chord progressions as numbers? The most common chords to show up in basically any genre of Western music are the 1, 4, and 5 chords. These chords are the bread and butter of fiddle tunes. And when you look at the circle of fifths, you can instantly see the 1, 4, and 5 chords for any key.
Take C as an example. C is the 1 chord. Now look to the left of C. That’s F, the 4 chord. Now look to the right of C. That’s G, the 5 chord. Bam. Now you know exactly what chords to expect when you’re in a jam session and someone calls a “basic 1-4-5 song in C.” What about another common fiddle key, G? G is your 1 chord. Look to the left and you see C, your 4 chord. Look to the right and you see D, your 5 chord. It’s that quick and easy.
Why you need to know this: When you know the circle of fifths, you understand how keys and chords relate to each other and gain more of a grasp on how keys and chords work beyond just memorizing them. The circle of fifths will help you recognize common chord patterns, understand why chord progressions sound good, and predict what’s coming next in a chord progression. It will also give you the tools you need to play in any key and transpose licks and songs into different keys.
Where you can learn and review these things in Fiddle School: Lesson 11, Lesson 15, Lesson 31.
And with that, we’ve covered the vast majority of what you need to know about music theory as a fiddler. You’ll find that most theory topics that come up fit into one of the topics above (and that all the topics connect to each other). Knowing the information included here (and reviewing it in Fiddle School) will give you the tools and the lingo to keep up and ask the right questions as you learn.
One last point I want to emphasize: you know more than you think you do. Even when you’re not explicitly focused on theory, you’re internalizing the sounds and feelings of these concepts as you practice them. Even if you don’t know how to build an arpeggio yet, I’ll guess that you’ve played one before. Let yourself move at a natural pace as you internalize these theory concepts. It doesn’t have to come all at once (and it won’t). These things take time to digest and that’s normal. Enjoy the journey and stay curious!
Want to get access to all the learning resources mentioned in this article? Join Fiddle School here.