Melody

“A gut-string classical Spanish guitar, a sweet, lovely little lady. The smell of it. Even now, to open a guitar case, when it's an old wooden guitar, I could crawl in and close the lid.”
                          ― Keith Richards

The history of the guitar can be traced back over 4,000 years to "bowl harps" and "tanburs" from ancient Sumerian, Babylonian, and Egyptian cultures and can be found in museums around the world today.  Later, the Moors brought the "oud" to Spain and the Europeans added frets and called it a "lute",  a derivative of the Arabic word "Al'ud" literally translated as "the wood".  The name "guitar" comes from the Sanskrit word for "string" - "tar", later becoming the name for "4 strings",  or "quitarra" in early Spanish for a 4-string guitar.  By the beginning of the Renaissance the 4-course guitar became popular in most of Europe, until finally a 5th and 6th string were added, and finally, around 1850, the Spanish luthier Antonio Torres increased the overall size of the body, and altered it's proportions, where the instrument took on the more familiar shape that we know today.

Harmony

"Great art picks up where nature ends." 

                             ―Marc Chagall

I think we would all agree that, if we simply open our eyes, Art is everywhere in our life.  In it's simplest forms it is watercolor on cold pressed paper, acrylic paint on a canvas, a well composed picture, or a memorable piece of literature.  All of them are physical manifestations of something conjured up, and then physically created.  We can travel the world and witness sculptures from thousands of years ago, still bearing witness to its creator.  However, Music, is ephemeral.  It can be played on an instrument, live in the air for that moment, and then it is gone, like the vapor from our breath on a cold day.  Like much of all great Art....it can lift our spirit, change our mood, or simply fill us with inspiration.  Although I am truly biased, but I firmly believe "Music can move our souls through our ears on a different level ...than we can be moved by seeing all other forms of art through our eyes."

Rhythm

“Music gives a soul to the universe, wings to the mind, flight to the imagination
and life to everything.”
                                          ― Plato

It's been a part of our culture since as far back as we can date mankind.  And the guitar has been a truly unique vehicle to bring music to us.  It has entertained nobility, and is always seen as the instrument of choice to support  a minstrel's ballad sung to a lover.  Andres Segovia regaled over 2,000 people in Carnegie Hall without amplification in 1946, and it's the overwhelming choice to bring camping or to a weekend BBQ at the beach.  Technically considered a "percussive instrument"...these qualities can be heard in Flamenco, Rock, and Rhythm and Blues.   And the guitar is also a chordal instrument capable of generating beautiful harmonies heard in it's Baroque, Classical, Romantic, and Jazz repetoire.  All the while, one can't deny it's melodic qualities... able to breathe life into rich melody lines.   These are just some of the reasons that create the beauty and popularity of the guitar.