Its probably in Here somewhere...

Yeah, it's in here somewhere.

Try searching the Guitar Noise Lessons for something like "Building Chords."

Check out the C major scale...the C major cord (C E G) is the 1st, 3rd and 5th degree of the scale. If I understand it correctly, a major cord consists of the 1st, Major 3rd and Perfect 5th intervals of the major scale,...where a minor cord consists of the 1st, Minor 3rd and Perfect 5th intervals of the major scale...in the case of C, it would be C E G for C major and C Eb G for C minor.

It's because of choirs in the middle ages.

We started out with scales, and everyone just sang the same line - that's called monophonic music. Easy to follow, but kind of boring. As early as the late tenth century, music theorists were speculating what might happen if you had two notes at the same time. Around the year 1000 a composer or two tried it out.

Then they built the Notre Dame cathedral in Paris. Nice big place, well suited for large choirs. And that led to the Notre Dame School of Polyphony, and a style of music called organum... half the folks sang the original melody, half sang it higher. That gave a nice, rich, full sound to the choir. And it turned out the intervals that sounded really good this way were perfect fourths and perfect fifths - if one voice sang C, the next sang F or G. That gave three intervals to use (we already had the octave, simply because of different vocal ranges)

The next century (the 1200s) led to a lot of experiments at Notre Dame, which was really the hotbed of composition at that point. They developed things like clausulae, where one voice went up a whole step (C to D) and the other down a half step (like C to B). That introduced more intervals. Eventually this style developed into counterpoint, where two voices move independently.

If two voices were good, three or four might be even better. The earliest works here were probably rounds (like Three Blind Mice) where harmonies were incidental to the melody - we have manuscripts from the late 1200s showing round-type melodies in up to six voices.

Around 1300 a guy named Johannes de Grocheo decided you needed at least three notes to really sound like a full harmony. His ideal was still based on fifths and octaves - a 'chord' in his day would be C-G-C. Other sounds occurred as part of the melodies, but they resolved to this 'chord'.

Then along comes Jacques de Liege, who tried to catalog the stuff that happened in between those 'chords'. He noted that 'splitting the fifth' by putting a voice in between was especially pleasing... although he seems to have been more pleased by minor triads than major ones - and overall, greatly preferred 'old' music to the new stuff.

But Jacques' thoughts stuck. One reason is that music of his day used 'just intonation' - the note E would actually be slightly different depending on what key you happened to be in. And when sung, that note would make consonnaces with the root and fifth that are a lot more 'solid' sounding than those you get on a guitar or piano today - they followed the natural overtone series.

So chords are variations of 1-3-5 because they sound good. They've got at least three notes because Johannes said they should, and the newest part of a chord is the third, because Jacques thought it made sense to split the outside interval (he also noted that sevenths should really be filled out by a fourth in between, anticipating the quartal harmony of the 1900s by 600 years)

Of course all of this is the Western approach. But there was a clay tablet unearthed in Syria that shows music with harmony, and in a major key that dates to about 1300BC - until that discovery, we credited the whole idea of scales to the ancient Greeks, and the development of major scales to only around 1300CE. Turned out they'd just reinvented something a whole lot older. Maybe future discoveries will lead us back to the guy banging two rocks together as the founder of chord theory.