I tried to look for something clear and unambiguous but I can't find it, or I'm missing something simple. The questions is: What do all chords have in common, and is there a set of rules allowing to say that these 2...N pitches are for sure a chord?
I know that most of chords contain at least 3 pitches, a Root , third and fifth, but as far as I understood this is not essential for every chord.
The other definition I read that a chord is a harmonic composition of at least 3 pitches which belong to the same scale, but it would mean that any 3 pitches from the for instance Chromatic Scale form a chord, which I guess is not true?
So - is there any rule which would allow me to form any possible chord (not just some subset of them) on guitar?
Or in the end it turns out that the list of chords comes rather from history/tradition and cannot be exactly described by a strict mathematical rule (like it is possible for instance with semitones in octave which can be mathematically described and mapped to frequencies of the sounds ? )