Where do chords come from? Απο που προέρχονται οι συγχορδίες;

Ολα προκύπτουν απο το μπαςο. Everything is derived from the bass.

Και απο την κλίμακα απο νοτες στην οποία ειναι γραμμένο το μουςικο κοματι.

And from the note scale the piece of music is written from.

Scale is the set of usually 7 notes the piece is composed from.

For example:

Imagine - John Lennon or Let it be - Beatles, Concerto for piano no 1 in C major - Motzart are all written in C major. The white keys of a piano keyboard, just these 7 white notes.

The chords defined by C major are: 

CEG ie C Major

DFA D minor

EGB E minor

FAC F major

GBD G major

ACE A minor

BDF

If on the other hand a piece is written in E minor when the bass is D the chord will be D major since this scale has the F sharp.

For example: We are the people - Empire of the Sun

Just the bass can define the whole chord.

Usually the rule 135 is used. Which defines minor or major chords.

For example (still assuming the E minor scale), C bass can define CEG ie the C major chord.

Usually other intervals are added to the bass in ingenious pieces:

7th (with it the 3rd is taken too)

6th (with it the 3rd is taken too)

9th( with it the 3rd is taken too)

For example (still using the E minor scale) C7 will mean CEGB ie the C major 7th chord.

This chord actually takes place at the beautiful moments of We are the People - Empire of the Sun when the bass becomes C.

Other examples of Cmaj7 when the scale is E minor is Breathe - Pink Floyd, Julia - Pavlov's Dog, Year of the Cat - Al Stewart

Scales are important. An easy way to remember them is the trick of adding a 5th to find the next more complicated one with more sharps. For example C major scale has all write keys. Next is G major scale which has one sharp, ie F# or the back key to the right of F. The next in complexity is D major scale which has C# and F#. Note how adding 5th helps us to find not only the next scale in complexity but what the sharp note will be!

It also follows that in order to play most pieces on a piano or really anywhere what we need to play is just the melody on the right hand and the single also note of bass on the left hand, bass is a melody too. The rest, the harmony is just made by adding 3rds, 5ths or 3rds, 6ths, or 3rd with 7ths or 9ths as the composer wishes.

References:

http://normanschmidt.net/scores/bachjs-general_bass_rules.pdf

Harmony - Piston

Musical Acoustics - Donald Hall