Music Theory Guide

Hi! My name is Abdullah. I’m a web designer and developer, and I am passionate about music and music theory. I wrote and built this interactive guide to make learning music theory fun and engaging. The keyboard at the top is playable. You can use your mouse, keyboard, or touchscreen to press the keys. You can also click any (Listen) button in the guide and the keyboard will play the associated notes.

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Look at the piano above. You’ll see that the white keys are labelled C, D, E, F, G, A, B, and then go back to C. Most of the white keys also have black keys between them. There are, in total, 12 keys that repeat. Note that there is no black key between B and C, or between E and F.

Each black note actually has two names. The note between C and D is called C sharp or D flat. (‘Sharp’ in music notation is written as ♯, and ‘flat’ is written as ♭). The word ‘sharp’ means that you go up one note, so one note up from C is C♯, one note up from D is D♯, etc. The word ‘flat’ means that you go down one note, so one note down from B is B♭, one note down from D is D♭, etc. We say that A♯ and B♭ are enharmonic notes, because they’re actually the same note with different names—in other words, A♯ and B♭ make the exact same sound.

The distance between two notes is called an interval. The smallest possible interval is between two notes that are right next to each other. This interval is called a semitone, which is also known as a half step. For example, the distance between C and C♯ is a semitone, as is the distance between C♯ and D.

The distance of two semitones is called a tone, which is also known as a full step. For example, the distance between C and D is a tone.

Each interval size has its own name:

An interval of 1 semitone is called a minor second. (Listen)
An interval of 2 semitones is called a major second. (Listen)
An interval of 3 semitones is called a minor third. (Listen)
An interval of 4 semitones is called a major third. (Listen)
An interval of 5 semitones is called a perfect fourth. (Listen)
An interval of 6 semitones is called an augmented fourth or a diminished fifth. (Listen)
An interval of 7 semitones is called a perfect fifth. (Listen)
An interval of 8 semitones is called a minor sixth. (Listen)
An interval of 9 semitones is called a major sixth. (Listen)
An interval of 10 semitones is called a minor seventh. (Listen)
An interval of 11 semitones is called a major seventh. (Listen)
An interval of 12 semitones is called an octave. (Listen)

Scales are made up of a specific formula of semitones and tones. The major scale, which is the most important scale in Western music, has the following formula:

tone - tone - semitone - tone - tone - tone - semitone

So, to play the C major scale…

You start from C, then go one tone (i.e. two semitones) up, which means that you skip C♯ and play D.
Then you go another tone up and play E.
Then you go one semitone up and play F (remember that there’s no note between E and F, so they’re only a semitone apart).
Then you go one tone up and play G.
Then you go one tone up and play A.
Then you go one tone up and play B.
Then you go one semitone up and play the C that’s an octave higher from the first C.

So the C major scale is C D E F G A B C. (Listen)

You can start on any note and play the major scale of that note using the same formula. So, for example, if you want to play the D major scale, you follow the same formula and get D E F♯ G A B C♯ D. (Listen)

Each major scale has a relative minor scale. What this means is that each major scale has a minor scale with the exact same notes. The only difference is that the minor scale starts on the sixth note of the major scale. For example, to get the relative minor scale of the C major scale, you start on the sixth note of C major, which is A. So we say that the A minor scale is the relative minor scale of the C major scale.

This also means that the minor scale has its own formula, which is actually just the formula of the major scale but rearranged so that you start on the sixth note. This formula is the following:

tone - semitone - tone - tone - semitone - tone - tone

Notice how this is actually just a rearrangement of the major scale. If you start from the second to last note in the major scale formula then circle back to the beginning, you get the formula for the minor scale.

The minor scale is called minor because it has a minor third (its third note is three semitones away from its first note). The major scale, on the other hand, has a major third (its third note is four semitones away from its first note).

A chord is a group of three or more notes that are played together. You get the notes of each chord from the scale that it comes from. For example, the notes of the C major chord are derived from the C major scale. What you do is play a note and skip a note. So to get the C major chord, you play C (the first note), skip the D, play the E (the third note), skip the F, and play the G (the fifth note). This means that the C major chord is made up of the notes C - E - G. (Listen)

You do the same for all notes. So, for example, if you play the first, third, and fifth notes of the D minor scale, you get the D minor chord, which is D - F - A. (Listen)

Each scale has a collection of chords. For example, because all the notes in the D minor chord are also in the C major scale, the D minor chord is actually also in the C major scale. On the other hand, the D major chord is not in the C major scale, because the D major chord has F♯, which is not in the C major scale.

The difference between a major chord and a minor chord is that the second note in the chord is one semitone higher in the major chord. In other words, the first and third notes in a major scale are 4 semitones—i.e. a major third—apart, and the first and third notes in a minor chord are 3 semitones—i.e. a minor third—apart.

To understand why this is, look at the formula for the major scale and compare it to the formula for the minor scale. When we follow the formula for the major scale starting from D, we get D - E - F♯ - G - A - B - C♯ - D. So the first, third, and fifth notes are D - F♯ - A. This is the D major chord. However, when we follow the formula for the minor scale starting from D, we get D - E - F - G - A - B♭ - C - D. So the first, third, and fifth notes are D - F - A. This is the D minor chord.

Just like there’s a formula for the notes on each scale, there’s also a formula for the chords in each scale. The formula for the chords in the major scale is the following:

major - minor - minor - major - major - minor - diminished

This is also written as the following:

I - ii - iii - IV - V - vi - vii°

(The capital Roman numerals are major chords. The small Roman numerals are minor chords. The seventh chord has a little O symbol, signifying that it’s a diminished chord.)

So, for example, in the C major scale, we have the following chords:

I: C major
ii: D minor
iii: E minor
IV: F major
V: G major
vi: A minor
vii°: B diminished

Okay, but hold on just a second! What’s a diminished chord?

We saw that a major chord is made up of the first, third, and fifth notes in the major scale. This means that the first and second notes in the chord are 4 semitones (a major third) apart, and the second and third notes are 3 semitones (a minor third) apart. We also saw that the minor chord is made up of the first, third, and fifth notes in the minor scale. This means that the first and second notes in the chord are 3 semitones (a minor third) apart, and the second and third notes in the chord are 4 semitones (a major third) apart.

Notice the formula here:

Major chord = major third + minor third

Minor chord = minor third + major third

However, if you look at the last chord in the major scale, you will see that it doesn’t follow either of these formulas. For example, in the C major scale, the last note is B. To play the B chord, you have to play B, skip a note, play D, skip a note, play F. So this chord is B - D - F. If you look at the interval between each of the two notes, you will see that it has the following formula:

minor third + minor third

So the interval between the first and second notes is a minor third, like the one in a minor chord. But unlike in a minor chord, the interval between the second and third notes is also a minor third. This is called a diminished chord, because the total distance between the first and third notes is smaller.

As you might have guessed, the chords in the major scale are also in the relative minor scale but starting from the sixth chord. For example, because the A minor scale is the same scale as the C major scale but starting from the sixth note, the A minor scale has the same chords as the C major scale but starting from the sixth note. In other words, the vi chord in the C major scale is the i chord in the A minor scale.

The following are the chords in the A minor scale:

i: A minor
ii°: B diminished
III: C major
iv: D minor
v: E minor
VI: F major
VII: G major

The circle of fifths is a very useful tool that shows how the scales and chords connect with each other.

Look at how the notes in the circle relate to each other: If you go clockwise, each note is a perfect fifth (7 semitones) away from the one before it. For example, G is a perfect fifth away from C, and D is a perfect fifth away from G. This is why it’s called the circle of fifths.

One of the magic uses of the circle of fifths is that if you play a major scale, then go to its fifth, and play the major scale of that note, all you have to do is add one sharp note. For example, we know that the C major scale is C - D - E - F -G -A -B - C. If we go to the fifth of this scale, we get G. So if we want to play the G major scale, all we have to do is add one sharp note. So every time we go one note clockwise on the circle, we have to add one sharp note.

The circle of fifths also shows us which note is sharpened. All we have to do is go two notes anticlockwise. So for G major, we go two notes anticlockwise in the circle and get F. This means that the G major scale has a sharpened F: G - A - B - C - D - E - F♯ - G.

Then we can go to the fifth of the G major scale and play D. If we want to play the D major scale, all we have to do is add another sharp note. To figure out which sharp note to add, we go two notes anticlockwise in the circle and get C. This means that the D major scale also has a sharpened C: D - E - F♯ - G - A - B - C♯ - D.

This goes on continuously till all notes in the scale are sharp.

We can also go anticlockwise from the top to figure out the scales that have flat notes. To know which note is flattened, we have to go to the note on the opposite end (six notes clockwise or six notes anticlockwise). For example, if we start from the top, we have C, which we know has no flats. The note next to C when we go anticlockwise is F. This means that the F major scale has one flat. To know which note is the flattened one, we go to the note that’s on the opposite end of F. This means that the the F major scale has a flattened B, which means that the F major scale has the following notes: F - G - A - B♭ - C - D -E -F.

If we move one more note anticlockwise from F, we get B♭. This means that the B♭ major scale has two flat notes. So we add the flat that’s already in the F major scale (which is B♭) then go six notes clockwise or anticlockwise to find out which other note is flattened. So we see that B♭ also has a flattened E, which means that the B♭ major scale has the following notes: B♭ - C - D - E♭ - F - G - A - B♭.

This goes on continuously till all notes in the scale are flat.

What all of this means in practice is that you can use the circle of fifths to change the scale that you’re playing. If you change from a scale to one right next to it in the circle, the change will be subtle, because there will only be one note difference. However, if you go from a scale to one further away, you can create a more drastic change in the music. It can create a dip or rise in the energy or the mood.

Just as you can play the same notes of the major scale starting from the sixth note and get the minor scale, you can also start from any other note and get a different scale depending on which note you start from. These scales are called the modes.

When you play the major scale starting from the second note, you get the Dorian mode. The relative Dorian of C major is D Dorian. You start from D and play the exact same notes as the notes in C major: D - E -F - G -A - B - C - D.

When you play the major scale starting from the third note, you get the Phrygian mode. The relative Phrygian mode of C major is E Phrygian. You start from E and play the exact same notes as the notes in C major.

Starting from the fourth note, you get the Lydian mode. The relative Lydian mode of C major is F Lydian.

Starting from the fifth note, you get the Mixolydian mode. The relative Mixolydian mode of C major is G Mixolydian.

Starting from the sixth note, you get the Aeolian mode. The relative Aeolian of C major is A Aeolian. This is actually just another name for the minor scale.

Starting from the seventh note, you get the Locrian mode. The relative Locrian mode of C major is B Locrian.

The major scale itself is also called the Ionian mode. So C major is also called C Ionian.

The modes are categorized into major or minor modes depending on whether the distance between the first and third note is a major third or a minor third. The major modes are the Ionian (aka the major scale), Lydian, and Mixolydian modes. The minor modes are the Aeolian (aka the minor scale), Dorian, Phrygian, and Locrian modes.

We saw earlier that we can make a chord by playing the first, third, and fifth note of a scale. For example, the C major chord is made up of the first, third, and fifth note of the C major chord, which are C - E - G. We can remove the third note (in this case, the E), and replace it with either the second or the fourth note of the scale. This would give us a suspended chord. For example, if we play C - D - G, we would get a C suspended second (Csus2) chord, because we would be replacing the third (E) with the second (D). If we play C - F - G, we would get a C suspended fourth (Csus4) chord, because we would be replacing the third with the fourth (F).

Suspended chords can act as transition chords. For example, if we want to go from D minor (D - F -A) to C major (C - E - G), we can play a Csus4 (C - F - G). This allows us to “suspend” the F in D minor by continuing to play it in Csus4, and then we resolve it down to E in C major: D - F - A → C - F - G → C - E - G. (Listen)

If you play the first, third, and fifth note of a scale, then also add the seventh note, you get a seventh chord. And just as with triads (note: a three-note chord is called a ‘triad’), seventh chords have different names depending on the intervals between them.

If you play a minor chord and add a note that’s a minor third higher than the fifth, you get a minor seventh chord. For example, if you play C - E♭ - G (C minor chord) and add B♭ (which is a minor third away from G), you get the C minor seventh (Cmin7) chord. Another way to look at this is to say that B♭ is a minor seventh away from C.

If you play a major chord and add a note that’s a major third higher than the fifth, you get a major seventh chord. For example, if you play C - E - G (C major chord) and add B (which is a major third away from G), you get the C major seventh (Cmaj7) chord. Another way to look at this is to say that B is a major seventh away from C.

If you play a minor chord and add a note that’s a major third higher than the fifth (i.e. major seventh from the first note), you get a minor major seventh (minMaj7) chord. For example, if you play C - E♭ - G, and add B, you get the C minor major seventh (CminMaj7) chord.

If you play a major chord and add a note that’s a minor third higher than the fifth (i.e. minor seventh from the first note), you get a major-minor seventh (majMin7) chord. For example, if you play C - E - G, and add B♭, you get the C major-minor seventh (CMajmin7) chord. A major-minor seventh chord is also called a dominant seventh chord. This chord is written with just the number 7. For example, C dominant seventh is written as C7.

Note that the dominant chord is the name of the fifth chord in a scale. For example, in the C major scale, G major is called the dominant chord. The dominant seventh chord is what you get when you play this chord plus a minor seventh from G. It’s the only possible major-minor seventh chord in the scale. If you play any of the two other major chords in the scale (C and F) with a minor seventh, you would go out of the scale. C7 has the notes C - E - G - B♭ (as we saw above), and B♭ is not in the C major scale. F7 has the notes F - A - C - E♯, and E♯ is not in the C major scale. In other words, the only possible major-minor seventh chord in a major scale comes from the dominant chord. This is why it’s called the dominant seventh chord.

You can play the notes in a chord in any order and still have the same chord. For example, you can play C major as C - E - G or E - C - G or G - C - E. These are called inversions, because you’re inverting the order of the notes in the chord.

When you play a chord in its original order, it’s called the root position.
When you play the chord with the third as the lowest note, it’s called the first inversion.
When you play the chord with the fifth as the lowest note, it’s called the second inversion.

Chord inversions can make music sound smoother, as they can reduce movement between the notes across the chords. For example, if you want to play C major followed by F major, if you play C major in the root position (C - E - G), then F major in the second inversion (C - F - A), you don’t have to move the C note, have to move only one note up from E to F, and two notes up from G to A. (Listen) On the other hand, if you play both chords in their root position, you have to move all notes five notes up: C to F, E to A, and G to C. (Listen)