Why we use modes??

So why do we need modes anyway? Isn't the major scale the same notes, so why would be want to learn new stuff? These were the biggest questions I had when I was learning Modes, and they are the questions that I would like to answer in this lesson...
In the last lesson we learnt about Diatonic Chords and the way that you can use Major Scale over any of the chords in the Diatonic Sequence for that key. So that is all good. But the Major Scale is a little bit "Orwellian" - all notes are equal, but some notes are more equal than others! ;) [this is a quote form George Orwell's fantastic book called "Animal Farm", if you have not read it them please check it out, it's fantastic!]. I can explain this to you but you also need to hear it too!
I'm going to give you an example using modes and chords that come from the C Major Scale.
You NEED to hear these examples and feel them for yourself so you need to get a mate to jam with or a looper pedal, or record yourself into something and then play it back. I highly recommend trying to find someone to learn this stuff with though, makes it way easier! Try and find yourself a "mode buddy" that you will study Modes with together, it will make the journey easier and a load more fun too!
Alternatively you could use this C Ionian track from my Really Useful Play Along Tracks. All those tracks will be very helpful through this course...
Lets start my talking about the C Major Scale played over a C Major Chord. That gives us C Ionian Mode (which I just call C Major, I think calling it C Ionian is a bit silly).
What you need to listen to is the way that each note of the C Major Scale sounds over the chord of C Major.
So lets start with a C Major Chord backing (either your mate playing C, or a looper pedal, or a jam track) and play each note of the scale very slowly and listen to the effect that each note has when played over the chord. Make sure you are aware of the notes as you play, so maybe say the note name out loud as you play the scale (so say C, D, E, F, G etc as you play them). This will help you remember the good and bad notes.
Ok - you done that? so if you did it well you probably noticed that there are some notes that sound a lot better than others. You probably found that the notes C, E and G sound perfect with the chord. You will probably have found the notes D and A a little tense, but kinda nice too. And I hope that you found the notes F and B quite dissonant and kinda wrong sounding. The B is actually quite a cool note in the right circumstance but not one that you would commonly stop on... but the F :( that is a yucky sounding note to stop on. To pass through it sounds great, but to stop a melody line on the note F while a C chord is playing generally sounds pretty horrible.
The reason for that is that it is the 4th degree of the scale - and played over the chord the 4th often clashes with the 3rd of the chord, mainly because they are a semitone apart. Lets look at all the notes in the scale (mode) against the chord to make that very clear... CT means Chord Tone.

	I	II	III	IV	V	VI	VII
C Major	C	D	E	F	G	A	B
C	ROOT CT	2nd	3rd CT	4th (yuk!)	5th CT	6th	7th

Now go and play the scale again and make sure that you are convinced that the CT notes are all real good and listen to how the 4th (F) sounds... Spend a bit of time with this if you really want to get this concept in your head. Learn to LISTEN not THINK. Your ears should be the judge of what sounds good, not your brain.
OK - hope you are still with me... so important point to remember:

All the notes of the scale are good, but some are better than others.

So now lets look at a mode - and we're going to look at playing a C Major scale over the 5th chord in the Key of C: which is G7. We would call this playing G Mixolydian, but that is not important now... we're just getting into why Modes are useful - worry about the names and all that later.
Now you need a G7 backing track (either your friend playing, or record your own G7, or use my G Mixolydian backing track) and you will again LISTEN to all the notes of the C Major scale being played over the G7 chord. So now you need to try it out (please actually do this - don't just read it) because that is the only way that you will really understand what I mean.
When you do that, you will discover that the notes that sound good over the G7 were very different from the notes that sounded good over the C... they are the same notes but each will have had a very different quality over this different chord.

	I	II	III	IV	V	VI	VII
G Mixolydian	G	A	B	C	D	E	F
G7	ROOT CT	2nd	3rd CT	4th (yuk!)	5th CT	6th	b7th CT

So if you listened well and played all the notes from the C Major scale over the G7 chord, you would have found that the Chord Tones (CT) G, B, D and F all sound great, A and E sound interesting, and C doesn't sound so good (it's the 4th clashing with the 3rd again). SO in this case the note C (which is the root note of the Parent Major Scale) is not a good note to play - and the note F (which did not sound so good over the C Major Chord) is great to play over a G7.
THIS IS WHY WE NEED MODES!
The notes from a C major scale can be played over a Cmaj7 chord and a G7 chord (if you understand basic diatonic theory you should be cool with this concept) but the RELATIONSHIP between the scale notes and the chords change. The quality of the note changes when the chords change.
Another example... the III chord in the key of C is E minor. Play a C note over that and it sounds well horrible!
Learning modes will help you play over chords, instead of thinking about keys. Which is very important when the keys change a lot, which happens a lot in jazz and modern blues.

Modes help us understand the relationships between scales and chords.

That is all it is. It's understanding why some notes from a scale will work well better over some chords than others. Now we are going to look more how to look at the modal theory (series and parallel) and then look at how you should practice them. Then we are going to look at each mode one at a time and look, practice and listen to what it sounds like and understand why and when we might use it.
I hope that gives you a better understanding of why we use modes.