What's the logic behind chords building patterns that are in key?

Question

I've found multiple resources on the internet that give you this pattern for building chords in a key, i.e. for the Major Scale:

1st Major, 2nd minor, 3rd minor, 4th Major, 5th Major, 6th minor, 7th Diminished, 8th Major.

I've found the fact that, for example when you're building a chord starting from the 2nd, it's a minor chord because the major chord would have a note that's not in the scale (F# for the key of C) and so on for the rest of the chords, is that all there is to it?

Answer 1

Triads are composed of thirds (i.e. when looking to a scale, start with a note, jump next, pick next, jump another and pick the next one)

Let's take a look at the C major scale (C, D, E, F, G, A, B):

C: C E G (C major)

D: D F A (D minor)

E: E G B (E minor)

F: F A C (F major)

G: G B D (G major)

A: A C E (A minor)

B: B D F (B diminished)

It works with any key, with minor keys, and if you stack four notes, you'll get 7ths chords.

Answer 2

The simplest way to find out how chords are built, is to take a note as a root (any note of the scale) and stack thirds on top of it.

In the C major scale, if you take D as the root and stack thirds on top of it, you'd get D minor: D -> F (minor third) -> A (major third) --> DFA which is the D minor chord.

Similarly for the major and diminished chords.

Also, if you want to add even more notes, you'd get 7th, 9th, 11th and 13th chords.

Answer 3

Stacking thirds is a common term for creating chords - triads are a good start point. C-E-G; D-F-A; E-G-B etc. The thirds arrive at a diatonic note each time - a note from that key.

However, it's not strictly that. In the triads you mention, it's actually a third and a fifth. The fifth being the next 'stacked third'. So this gives major or minor triads except for the one built on the leading note - here B. A perfect fifth (which the others all contain) would give a non diatonic note, so for the B chord, it'll be D (m3) and F (dim5).

Staying with the 'stacked thirds' idea, any triad can have two minor thirds, making a diminished chord; a maj and min third, making a major chord; a min and maj third, making a minor chord, or two maj thirds, making an augmented chord.

As Shev says, keep stacking those thirds (either maj or min) to produce 7ths, 9ths, 11ths and 13ths, with some interesting blends of notes.

Answer 4

That's all there is to THAT. To what triads are constructed from the unaltered notes of a scale. But don't fall into the trap of thinking that diatonic triads are The Truth, everything else needs special permission or explanation. There are plenty of chords beyond triads and the 'pile of thirds'. And many (most, even) of them use out-of-scale notes. Any system of theory that treats them as interlopers isn't going to take you very far.

Answer 5

I can't help but wonder if you are asking the wrong question. Modulation and borrowing chords from other keys is what makes music interesting. Most music 'modulates' or uses chords that are 'borrowed' from other keys. A piece of music might be in the key of C major, but it might use chords that are not 'diatonic' i.e. within the key signature. Or, it might 'modulate' to a different key for an extended period. I explained rules of harmony and modulation in Rocking Cowboy's question about the use of a bVII chord in a major key, in his example, and F chord in the key of G (major).

Here's the link: Why do many songs in major keys use a bVII chord?

Answer 6

If you really want to understand that, you have to know about scales and chord's patterns and most importantly intervals between degrees.
For example consider four triad chord structure (degrees showed by "Roman numerals"):

1) Major : I <2 steps> II <1.5 steps> III
2) Minor : I <1.5 steps> II <2 steps> III
3) Diminished : I <1.5 steps> II <1.5 steps> III
4) Augmented : I <2 steps> II <2 steps> III

and now lets see Major scale's structure :
I <1 step> II <1 step> III <0.5 step> IV <1 step> V <1 step> VI <1 step> VII <0.5 step> VIII

lets make some chords on simple C Major scale:
begin with one degree on scale and choose two other notes every other one:
if you begin with C you will have : C-E-G
take a look on major scale pattern : C <1 step + 1 step = 2 steps> E <1 step + half step = 1.5 steps> G so it's a Major chord. Very simple.
Note that you're making some chords on a specific scale and you have to choose your notes(degrees) from that scale.
If you want to know more deeply about these stuff , you need to learn about "Quality in musical interval"