You may have seen chord charts or lyrics sheets and maybe you can play the chords and different shapes but you don't know what all those numbers and stuff really mean.

We are going to unravel the mystery behind the symbols and we will see how understanding what they mean will help us memorize chord shapes on the guitar, transform one kind of chord into another or even find our own shapes and voicings.

We will start by saying that a chord is when we play three or more notes at the same time, but how do we choose which notes to play?

Everybody knows the C major scale, we just play all the white keys on a piano starting from C (which we will call the root) and it sounds really nice so it seems like a good idea to use notes from this scale to build our chords.

If we play the first three notes of the scale together, the sound will be a little strange, probably the notes are too close together, so we will start from C and we will skip the second note and play the third then we will skip the 4th note and play the 5th and now our chord sounds really nice. I guess that we all can hear that this is a Major chord, it sounds 'happy', calm and stable. If we do the same thing starting from F and from G we get the same result, a nice major chord. We used the 1st the 3rd and the fifth note in the scale but we could add more, like the 7th and the 9th, the 11th, and the 13th, always skipping one note at a time till we play all seven notes in the scale. Do all these numbers ring a bell? We could think that the numbers after a chord's name may have some kind of relationship with these notes that we will call the 'Degrees' of the scale: the first note is the first degree, the third note is the third degree, and so on.

You may object that a major scale just has seven notes and you'd be right, so we will introduce the concept of 'Interval' which is the distance between any two notes, counting those two notes and all the notes in between on the major scale: the interval C – G on the C major scale will be a Fifth, C – D – E – F – G = five notes and the interval F – A is a Third, F – G – A = three notes. The interval between any note and the next one with the same name is called an Octave.

We can measure intervals bigger than an octave: from C to F in the next octave is an Eleventh (C – D – E – F is four notes and we add seven for the octave), in the same way, a 9th is the same note as a second but one octave up and the 13th corresponds to a 6th. We don't use intervals bigger than a 13th as it would get unnecessarily complicated.

Now that we have a method to 'measure' the notes, let's see if we can find a formula to build our chords that is not dependent on the root’s name.

We already built 3 Major chords starting from C, F, and G using what we now can call a Third and a Fifth from each root and we could think that this is the formula for a Major chord but if we start from D, for example, and we play D, F and A (third and fifth) we get a totally different chord, it doesn't sound like a major chord at all.

But we used our formula! If we apply the formula and start from E or A we get the same kind of chord, and it's not a major chord, so maybe the way we measured the intervals is not really that good, we need something more accurate.

The mistake we're making is that we're only counting the white keys, but in reality, we also have black keys in between them and the smallest interval we can get is between a white key and the black key next to it, if there is one.

We will call this interval a halftone or semitone or half step and it's the smallest distance we can have between two notes in western music.

If we re-calculate our intervals now, we find that from C to E we have 4 halftones but from D to F we just have 3 so the two intervals are both thirds (they're made up of three white keys), but one is bigger than the other and calling them Major and Minor Thirds seems quite the right thing to do.

Major Third		Minor Third

The two kinds of Third determine a very radical change in sound, they divide the world of chords (almost) in two, so the interval from the root to the Third is the first thing that goes in a chord's name: if it's minor we'll add a minus sign or a lowercase 'm' right after the name (Am or A-). The distance from the root to the 5th remains unchanged, and it's actually 3 and a half tones in both cases.

Perfect Fifth		Perfect Fifth

This is true for all the chords we can build on the notes of the Major scale except for the one that we build starting from B: both thirds are minor, from B to D and D to F and so we will call this interval a diminished or flat 5th (three Tones).

Perfect Fifth		Diminished Fifth

We call three note chords 'Triads' and we can see that starting from each note of the scale we get three Major triads (C – F – G), three minor triads (D – E - A), and one diminished triad starting from B: this is an important theory concept that we will explore in another course where we will talk about scales and keys.

But do all other intervals 'move' like the third and fifth? To find out let's get back to our piano and consider the notes on the white keys, the C major scale: we could say that their positions, their intervals from the root represent the default status, some are called 'Perfect' (a perfect Fifth) and some are Major (a Major Third or Seventh). Every note can 'move' to the nearest black key and we can see that some can move in both directions (second, fifth and sixth) and the others only backward or forward.

The Third and Seventh can only move backward and we will call them Major and minor. The Fourth and Fifth in their default state (F and G in the C major scale) are called 'Perfect' due to physical and mathematical properties that we will not discuss here.

The Fourth can only move forward, from 'Perfect' to Augmented (or Sharp) while the Fifth can move in both directions to Augmented or Diminished (Flat). The Second and Sixth can also move in both directions to Augmented or Diminished but they are called 'Major' in their default state. Compound intervals (bigger than an octave) like 9th, 11th, and 13th retain the same properties as their counterparts one octave lower (2nd, 4th, and 6th) and when we name chords we can use one or the other unless we really want to be specific.

Now that we know more about intervals and their names we can circle back to chord construction and naming.

We already said that we can build chords starting from the root and adding notes one Third apart and that the first Third determines if the chord is Major or minor: the symbol 'C' refers to a chord with a major third and a perfect Fifth and we can see that when these two intervals are in their 'default' states they are not mentioned in the name. We can move the Third one halftone back and get a Minor chord (C- or Cm) but we could move that note even further back to D and we would 'lose' the third, we would get a 'Suspended' (Sus) chord that is neither Major nor Minor (Csus2 or Csus9, same note, different octave). A very common chord is the Sus4 and I hope the name is self-explanatory: we move the Major Third one step forward to get a Fourth. We can have a second or fourth in the chord together with the third (Minor or Major) but they're usually one octave apart (9th and 11th ) and that is reflected in the name: C9 or Am11, for example.

C7 means a C major chord with a minor 7th, C Maj7 (or CΔ or C7+) is a C major with a major 7th. Cm7 or C-7 indicate a minor chord with a minor seventh: the first ‘minor’ in the chord’s name always refers to the third while the minor 7th is just shown as ‘7’.

The Fifth can move both ways, it can be augmented or diminished and that will be reflected in the name by adding a ? (sharp) or b (flat) as in a C7#5 or C-7b5.

Presence and alterations of 9th, 11th, or 13th will be reflected in the chord's name, usually after the 7th, if present.

There is another couple of chords that I want to talk about. We saw that starting from B we get a minor chord with a diminished 5th and if we add the seventh note we get a minor chord with a minor 7th and a flat 5th that we will call B-7b5 or half-diminished or we can use a small circle with a slash through it (?) as a symbol. But there's a case where we can move the 7th back another half step (to a diminished seventh) and will get what we call a Diminished chord and the symbol is a circle. It's a very particular chord because all the intervals in the chords are minor thirds so every note in the chord can be the root of a different chord. We get four chords with the same shape on the guitar, or we can use the same shape, in the same position to play any of the four chords (A° - C° - D#° - F#° for example).

So to recap, we can build a major chord using the root a major third and a perfect 5th and we will name it ‘C', we can move the third back 1/2 step and get a minor chord and add a minus sign or we can move the third up 1/2 step and get a suspended 4th chord. We can move the third back a whole step, a whole tone, and get a suspended 9th chord. If we want a 7th chord, we add the seventh note: we can move the octave back a half step for the major 7th and a whole tone for the minor 7th and another halftone if we want a diminished 7th. We can add any degree of the major scale and we can alter it, we can add a flat nine we can add a sharp five and we know that it will be reflected in the name of the chord, in the number, or in other symbols like 'sus'. So the relationship between chords names and the notes that they are made from is a very simple one and follows the movements of the notes inside the chords. This is going to be very useful when we will study chord shapes on the guitar to memorize them, not just as different, totally separate entities, totally separate shapes but as something that flows from one shape to the other, and has a logic to it.

Appendix one

chords names, symbols and component intervals

Appendix two

Scale degrees and interval names