Question: My question relates to the chord pattern formulas.

For this Example we are commonly given these two formula patterns as one of the steps to construct chords in a key. I have been self teaching/learning and can't seem to find any information on the web to explain how these patterns are derived?

For the Major scale = {Maj, Min, Min, Maj, Maj, Min, Dim} is used to build the chords in a key

For the Minor scale = {Min, Dim, Maj, Min, Min, Maj, Maj} is used to build the chords in a key

Anyone who can shed light on this part I would really appreciate.
Thanks

Answer: 
Trying to encapsulate an answer that's concise and short!

Triads are basically '*stacked thirds*'. That is, notes 1,3,5, and 2,4,6, and 3,5,7 etc.It is a fact that each root is from a diatonic note in that key. Thus 1,3,5 in key C is CEG; 2,4,6 is DFA, 3,5,7 is EGB etc.Some of those 'thirds' intervals are major (M), others minor (m). One has both intervals minor, (d) - diminished.

That gives a sequence of M m m M M m d, as others say.

Start the sequence on the last m - m d M m m M M - same order, different start point. So, really, one pattern!
The patterns derive from the three note triads built on each tone of the gamut of letters `A B C D E F G`. You call these the *diatonic* triads...

[![enter image description here](https://i.stack.imgur.com/J17pu.png)](https://i.stack.imgur.com/J17pu.png)

...notice that the pattern is really *one pattern of seven chords* where major and minor are just segments within that seven chord pattern.

The seven chord pattern can theoretically ascend or descend infinitely which is represented visually more easily as a circle...

[![enter image description here](https://i.stack.imgur.com/bcaOI.png)](https://i.stack.imgur.com/bcaOI.png)