erm well they say the 5th 7th and 12th threats are ure harmonics but really... you can get one on every string more or less... depending on ure pickups and amp and how good you are... but its not really hard 2 basic ways number one just slip your finger over a fret erm say the 5th fret but the key is to not acually push the string in just hold it gentle and pick... now try this anywhere on the board and lisen the sounds... the second way is to kinda choke your pick... what i mean is hold it close to the end so when you pick the string it almost traps between your finger and pick... this does take a few minits to get used to. there is other ways like erm just hit a open string and ever so gentley touch the string on the 5th fret or 3rd 4th what ever dont push it into the fret bord justplace ure finger over the top and then bring it back off... ldz of diffrant wayz
Music theory of or relating to...well...harmony. Chords, scales, arpeggios, figured bass, all that fancy stuff. Just about anything theory-related that doesn't have to do strictly with rhythm.
I ll try and sum up harmonic theory.

Its the study of how intervals sound when played together and how they relate to other intervals being sounded together.

How chords relate to one and other to form harmonic progressions.

Thats a very basic veiw of it though.
Sat in a lab, curing diseases. They actually LET me play with chemicals!