The Difference Between Traids and 7th Chords
 
To put it simply, Triads are chords that have three unique notes and 7th Chords have four. Triads can have the following colors: Major (happy), Minor (sad), Diminished (scary), and Augmented (mysterious).  7th chords on the other hand can be Major, Minor, Dominant (asks a question), Half Diminished, and Fully Diminished. The 7th Chords from an earlier lesson in this section were all Dominant.  For each Dominant 7th chord question there is a Major or Minor Triad that is the answer.  You've no doubt heard this over and over again in music.  Play the following chords and note how it sounds like a question followed by an answer:

E Dom 7th
|O---|---|---|---| Question
|O---|---|---|---|
||-1-|---|---|---|
|O---|---|---|---|
||---|-2-|---|---|
|O---|---|---|---|

A Major
|O---|---|---|---| Answer
||---|-3-|---|---|
||---|-2-|---|---|
||---|-1-|---|---|
|O---|---|---|---|
|X---|---|---|---|
 
Here is another example:

A Dom 7th
|O---|---|---|---| Question
||---|-2-|---|---|
|O---|---|---|---|
||---|-1-|---|---|
|O---|---|---|---|
|X---|---|---|---|

D Minor
||-1-|---|---|---| Answer
||---|---|-3-|---|
||---|-2-|---|---|
|O---|---|---|---|
|X---|---|---|---|
|X---|---|---|---|
 
Now go back to the sections on Major, Minor, and Dom 7th chords and see if you can find the right answer for each Dom 7th question.