It seems the position of a chord's notes on a guitar fret board should obey some rules!
As an example; why, in Cm chord, the G note on lower E String is not in count?
I'll be thankful if anyone can help me in realizing such rules (, if existing)...
On guitar, due to its tuning, sometimes there is little choice as to how some chords are voiced.
The root 'inversion' of a chord is the strongest sounding, as the root note is the lowest heard.
There is nothing at all wrong with playing a 1st or 2nd inversion of a chord, on guitar or any other chordal instrument.
On guitar, there are really only two major chord shapes which incorporate the bottom string playing the root . E shape and G shape, both completely moveable up the neck.
A shape and C shape have the root note on the fifth string, although another note from the chord is playable on the bottom string.
Playing the chord as a six string version is not a 'mistake', and is quite acceptable - although a lot of guitar driven websites seem dutybound to state that those chords must be played without the bottom string sounding at all. Thus missed or muted.
When strumming, it's often difficult to not play that 'wrong' string, so it's not inconvenient to leave it as part of the chord, where it will still be in tune with the rest of the chord, merely producing a different voicing, in its inversion.
Use it (if it's in tune!), and it's not wrong! Sometimes it's actually a good thing to have a different lowest note in a chord somewhere in a song!
Chords are usually played (or described) in root position, e.g. for a-c-e you don't play the bass-string E.
But if you want to play an inversion (Am46) or the change of 4th in the bass line: a-e-a-e then the E-string has to be picked too.
The same constellation you have in C major or c minor and all other chords.
If you play the open strings of your guitar tuned E-A-D-g-b-e you have almost an Em chord: Em = egb ... Now you have in your open strings already E (6) ....g-b-e. (3-2-1 these are the numbers of the open strings) A and D are not elements of the Em triad and can only be changed by augmentation (pressing 2 fingers in the 2nd fret of and shorting the string length of the A and D string: So we get another b and another e). If you continue this method you will find numerous chord pattern for the same triad or tetrad. (There are no rules - except you play i.g. the a minor or the E major chord with your fingers 2,3,4 and move them as barré chords with the index finger from fret to fret - you can also do so with the G major chord, C major, D7, A7, e minor or the diminished chords.
here are some examples of simplified chords where you might develop the tones that are played:
Writing them down, notating in a staff system and comparing with the keyboard pattern will help you to understand the principle and to transpose them fret by fret (a halftone ) higher.
https://nationalguitaracademy.com/easy-guitar-chords/
Root position and inverted chords A chord is in root position if its root is the lowest note. This is sometimes known as the parent chord of its inversions.For example, the root of a C-major triad is C, so a C-major triad will be in root position if C is the lowest note and its third and fifth (E and G, respectively) are above it – or, on occasion, don't sound at all.
more information you'll find here:
https://en.wikipedia.org/wiki/Inversion_(music)#Inverted_chords
