A Beginner's Guide to Modes & Their Characteristics

Hey guys. Check out my article on an introduction to modes and their characteristics. Let's stop being scared... Together.

Ultimate Guitar
Since the dawn of time, modes have freaked people out. The pretentious and pompous musicians have used their modal knowledge to look down smugly and dismissively from their pedestal. I'm here to tell you that a mode is nothing more than a scale or family of notes that will work over certain chord progressions and situations. In layman's terms: "Play these notes here and it won't sound s*%t!".

Let's take a look at every mode relative to the key of "C" so that we're only dealing with natural notes (no sharps or flats). I want to look at Ionian and Aeolian first as they are the most common and will help with the learning of the other modes.

Mode 1: Ionian

"C" Ionian: C D E F G A B C (standard MAJOR scale)

Mode 6: Aeolian

"A" Aeolian: A B C D E F G A (standard NATURAL MINOR scale)

Have a play through both of these scales, The reason why I wish to go over these 2 modes first is that you've probably heard or played them many times before. They're the most common of modes we hear in music today and are the main staple for our basic "happy" and "sad" sounding modes. We'll be using both of these "more common sounding" modes, and comparing them to the daunting and more interesting modes, to hear the nuances and characteristics that differentiate them from each other. Let's look at these other 5 modes relative to "C".

Mode 2: Dorian

"D" Dorian: D E F G A B C D (MINOR scale with sharp 6th)

You'll notice the raised 6th in the Dorian scale is a lot more positive sounding than the 6th note of the Aeolian scale.

"D" Aeolian: D E F G A Bb C D

The straight minor 6th from Aeolian is a lot sadder and darker. Below are some references to some Dorian songs for you to hear the mode's characteristics at work!

Some Dorian songs:
  • "The Extremist" - Joe Satriani
  • "Whatta Man" - Salt N' Pepa
  • "Mad World" (chorus) - Gary Jules
  • "Classical Gas" (chorus section) - Williams Mason

Mode 3: Phrygian

"E" Phrygian: E F G A B C D E (MINOR scale with flat 2nd)

You'll notice the flat 2nd in the Phrygian scale is a lot more tense and evil sounding than the 2nd note of the Aeolian scale.

"E" Aeolian: E F# G A B C D E

The straight minor 2nd from Aeolian is a lot more neutral and less abrasive. Below are some references to some Phrygian songs for you to hear the mode's characteristics at work!

Some Phrygian songs:
  • "Symphony Of Destruction" - Megadeth
  • "Wherever I May Roam" - Metallica
  • "Over the Wall" - Testament

Mode 4: Lydian

"F" Lydian: F G A B C D E F (MAJOR scale with a raised 4th)

You'll notice the raised 4th in the Lydian scale is a lot more tense and somewhat quirky sounding than the 4th note of the Ionian scale.

"F" Ionian: F G A Bb C D E F

The straight major 4th (or perfect 4th) from Ionian sounds a lot more neutral and typical. Below are some references to some Lydian songs for you to hear the mode's characteristics at work!

Some Lydian songs:
  • "Curve" - John Petrucci
  • "Flying in a Blue Dream" - Joe Satriani
  • "The Simpsons Theme" - Hans Zimmer
  • "Dreams" - Fleetwood Mac

Mode 5: Mixolydian

"G" Mixolydian: G A B C D E F G (MAJOR scale with a flat 7th AKA dominant 7th)

You'll notice the flat 7th in the Mixolydian scale is a lot more rocking and fist raising then that of the regular major 7th note of the Ionian scale.

"G" Ionian: G A B C D E F# G

The straight major 7th from Ionian sounds a lot more coy and unresolved. The flat or dominant 7th sound from the Mixolydian scale has more of a stadium rock sound and can sometimes also sound Celtic or even a bit Elvish! Below are some references to some Mixolydian songs for you to hear the mode's characteristics at work!
  • "Nothing But a Good Time" - Poison
  • "Glasgow Kiss" - John Petrucci
  • "Sweet Child O' Mine" - Guns N' Roses

Mode 7: Locrian

"B" Locrian: B C D E F G A B (MINOR scale with flat 2nd and flat 5th)

You'll notice the flat 2nd and flat 5th in the Locrian scale sound evil, darker and basically just more gross then that of the regular 2nd and 5th note of the Aeolian scale. Think about all those evil chords or notes (generally flat 5ths) in Metallica and Black Sabbath riffs, then add the semi tonal evilness and tension of the "Jaws" theme.

"B" Aeolian: B C# D E F# G A B

The straight minor 2nd and 5th from Aeolian are obviously less evil and have a more naturally sad sound. Keep in mind that this is the least common or used mode. It's use generally results in pretty yucky sounding riffs and chord progressions. Below are some references to some Locrian songs for you to hear the mode's characteristics at work (gross as they may be)!
  • "Raining Blood" (chorus section 1:39) - Slayer
  • "Painkiller" - Judas Priest
  • "Like a Surgeon" (chorus section) - Ciara
I hope this has got you guys on the right path to begin your modal musical journey. Happy shredding!

By Chris Zoupa

90 comments sorted by best / new / date

    Call me stupid, or whatever, but i don't understand anything. How is this used, what do chords behind it mean, why are these modes same thing as the one scale, but called differently , i really don't understand the concept of modes, it is something , but it isn't... I can play guitar quite well, but these theoretical things i just can't grasp.
    This, I still don't understand the difference between a mode and scale. The Aeolian and Dorian modes seem to both come from the Minor Scale?
    The problem here is that everyone teaches modes without teaching music theory. There is a parent scale, in this case the major scale used in diatonic harmony. The modes are derived from the parent scale without alteration just as the chords are. In truth there is only the major scale and the sounds you can derive from it by harmonizing each note individually forming the basis of chord structure: Every "mode" listed is the C major scale played over its respective chord. C(Ionian/Major) Dm(Dorian) Em(Phrygian) F(Lydian) G7(Mixolydian) Am(Aeolian/minor) Bdim(Locrian). Without delving into too much theory, the C major scale played over a single chord listed above will result in the modal sound unique to each. Of course there are ways to create chord progressions that will bring out the sound more than others. So you don't need to learn a gazillion scales, just learn your major scales and how they relate to the chords.
    That's true if the song you are playing is in Ionian mode.In reality every mode has a certain chord progression that helps it establish it's sound and it's character. The Ionian mode for example has the infamous I,IV,V,I chord progression that helps it establish it's sound as a "happy" scale.So in C Ionian we have C/F/G/C.Of course you could play Lydian over F and Mixolydian over G,but the overall sound would be that of C Ionian,or as we simply call,C Major. The Phrygian mode however has an entirely different chord progression to establish it's sound as an eastern,mystical scale.It's the I/II/VII/I which in E phrygian would translate into Em,F,Dm,Em.Now E phrygian may have the same notes as C Ionian,but now we think of E as the root,because that's where the music resovles,thus in the previous chord progression Em is the I instead of III.
    It doesn't matter what mode you are using, the theory is derived from the diatonic harmony of the major scale. If you are playing A Dorian mode you are really playing the G major scale and the chords would also relate to the harmonized scale it was derived from. And FWIW, there are no set modal progressions.
    If you are playing A dorian over Am on a chord progression like this G/Am/C D/G then yes. But if the chord progression is resolved around Am,using chords from G major,then you are essentialy playing in A Dorian.At that point A Dorian is not a mode.Is a scale on it's own with it's totally unique sound,despite having the same notes as G Major.
    But the harmony and theory are the same and that first progression you list is derived from G major anyway so I'm not sure what your point is. Just because it sounds different doesn't change the fact that it is still G major. But hey, there are twelve keys, so if you want to learn theory for 84 scales instead of just 12 then go right ahead.
    So by your point Beethoven's Moonlight Sonata is in E major,not C# Minor because C# Aeolian has the same notes as E Ionian.And so does every minor song in existance. My point is that you can use modes in two ways. The first one is to use them in order to solo over the corresponding chord in a chord progression. The second is to base entirely your chord changes around the mode you want,in order create a total different sound and feeling. The difference is the tonic and how the song resolves around it.C Major and E phrygian might have the same notes but if I base my chords and melody around C will result in a tottaly different sound than if I use the same notes to base my chords/melody around E.This is why each mode has their own very unique and recognisable sound.Because I can use the same notes to base my songs to a variety of "central points" which in music we call tonic.
    To understand it more try to play with your instrument the following chord progressions in order to hear the differences. C/Em/Am/Dm G7/ Now the next chord your brain wants to hear is C again which means you based your song around C and just have wirtten a song in C Ionian or C major. You can of course use C Ionian,E Phrygian,A Aeolian,D Dorian and G mixolydian to solo over the chords.The song might temporally change mood and sound depending on the chord changes but in the end it will always have the character of C Major. Now try playing this.Same notes,same chords as C major scale,different order. Em/F/Dm/Em Notice how when you play Em again your brain has that "complete" feeling?You just based a Song around E using notes from C Major,thus your song now is in E phrygian.
    Listen to yourselves! This kind of explanation doesn't help anyone, except those who already understand modes, and they don't need any more explaining. The more i read your answers,the less i understand. xD
    Yeah lol,I'll agree with you.Understanding modes doesn't happen overnight and no matter how good a teacher is,it will stil require some effort from your part to grasp the concept. The more you play them and the more you analyse songs,the more you will start understanding them by yourself.There is just way too much information for your mind to grasp just by reading an article.
    thanks a lot for taking the time to write all that BlackRose93. Before reading everything you just said, I sort of thought of modes as 'pointless' because C Ionian and A Aeolian, for example, have the same notes, so i thought it would be fine to just know the C major scale and be done with it. But now I see how resolving to or basing your chord progression on a different chord other than its parent scale's main chord creates a different feel and sound.
    Scales are modes. The Aeolian scale is the minor we use the majority of the time. The Dorian, however, does not come out of the Aeolian. It's an extension of the Ionian. Here's another way I use modes... When I'm playing with a band and I'm given a chord progression I gotta know what mode to use for my leads. If the progression is simply G,B,F,D,G then I know I have to write fills using the mixolydian scale in G. If I played a Gm scale the Bb would clash. Using a BMj wouldn't work because of the F#. You simply have to know the modes in order to be a good player. It separates the men from the boys.
    Every mode is either major or minor sounding.That depends on the 3rd of the mode. C Ionian ,C is the root,E the 3rd=Major 3rd=Major scale D dorian ,D is the root F the 3rd=Minor 3rd=Minor scale E Phrygian ,E is the root,G the 3rd=Minor 3rd=Minor scale F lydian ,F the root,A the 3rd=Major 3rd=Major scale G Mixolydian ,G the root,B the 3rd=Major 3rd=Major scale A Aeolian ,A the root,C the 3rd=Minor 3rd=Minor scale B Locrian,B the root,D the 3rd=Minor 3rd=Minor scale As you can see there is not just one Major or Minor scale.We just call the Ionian the Major and the Aeolian the Minor because those are the ones we use the most.In Jazz music however,Dorian is the default Minor scale most of the time.
    I think a big part of the confusion is that modes are all taught relative to the C major scale, i.e. this is C Ionian, this D Dorian, this is E Phrygian. This leads to the " What's the point of having 7 different names for the same group of notes". I now I stumbled over that for years. What broke me out is playing each mode BASED OFF THE SAME ROOT... i.e. C Ionian, C Dorian , C Phrygian. etc.. Once I did this I was able to hear the differences and flavors each mode had to offer based on the intervals within it.
    I think that the "off-one-root" approach and "relative-mode" approach are equally good in assimilating and visualizing the intervallic structure of the modes but more importantly, I think that the part that wasn't introduced and still missing in this first lesson is the discussion of the tonal center and the function, (strengths and weaknesses) of the other notes with respect to the tonal center of a mode. . A working knowledge of modes doesn't end up with something like merely knowing that the C major scale has seven notes - C, D, E, F, G, A, B and that the D Dorian mode and E Phrygian modes have the same 7-notes or chords played with a slightly different orientation. It would be good to show short examples of licks/riffs defining each mode in a modern-day context. Overall, a good video and introductory lesson on modes
    That really cleared up modes for me. I agree with Grarfield, using the song examples was a useful idea.
    Hi Chris - is there going to be a part 2 to this one? I think that whilst most people can agree on the notes/formula of different modes, a lot of people misunderstand how they are actually used. I "think" what you're going for is using modes to visualise accidentals to the major amd minor scales rather than traditional modal songs but it doesn't come off as very clear within the article.
    My guitar teacher many many years ago taught me the following acronym to remember the order of modes... I Don't Play Like My Aunt Lucy Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aolean, Locrian. Instantly remembered the order.
    "I'm here to tell you that a mode is nothing more than a scale or family of notes that will work over certain chord progressions and situations" That's not entirely accurate. Because in "modal" music, Chord Progressions aren't really a thing. While the C Major scale shares the same intervals as C Ionian, a song in C major is not the same as a song in C Ionian. If I just played a C major chord or a C drone and played the C Ionian mode over it, that will give you the "Ionian" sound. If you change the tonal center (as you do with a chord progression) your harmony will inevitably pull back to the tonic chord and you will lose the modal sound. I suppose that what this lesson is trying to teach is what modes are in simple terms and for that purpose, this is good.
    steven seagull
    Anyone who overstresses the importance of modes, or indeed thinks they "separate the men from the boys" simply doesn't understand them properly.
    Are you saying they're not important?
    They are important, but people overstress modes and forget how important their ears are. You don't need modes to be a great player, you need good ears.
    All of you are great! I think I learned more by reading comments and feedback than I did the actual lesson, which was also great. Years ago I tried teaching myself guitar from what I had learned in high school band resulted in nothing but power chords and 1st position pentatonic minor left me frustrated and bored with playing. Now 20 years later, getting back into that longing to play. I have learned more in 1 year than I did in the 5 years. A whole bunch of it is still Greek to me, but man did you all through a lot of theory out there.....You all made my day! Thanks a Bunch!
    Modes are tempting, but in this day and age surely a solid understanding of tonal harmony is all you actually need. Then all you really need to understand are the Major and Minor scales because you will also understand how accidentals can affect the sound. It is by no means an easy task, but I suggest this is easier than assigning particular accidentals to a modal name. After all modes are so last year (read few centuries).
    There is a difference between natural minor and modal minor when you are dealing with harmony. But this was a great lesson. Kudos to Chris for getting everybody to hear the individual characteristics of each mode. They aren't supposed to be thought of as derivatives to a scale. If you want to see them as something related to other scales then this is the way to go. The parallel approach. E Phrygian sounds different to E modal minor. And THAT is the way to look at modes. Not thinking of them as things to use in key. 10/10 lesson
    Chris Zoupa
    Thanks dude. I don't like the RELATIVE approach. You've got to express the characteristics and quirks of the mode. Listen to the simpsons theme. It's quirky and weird because of the #4/b5 and that's why it sounds so Lydiany!
    My favorite (and only) example of playing modally is Miles Davis' So What? D Dorian 16 bars D# Dorian 8 bars D Dorian 8 bars Sweet sweet licks
    CDEFGABC - Ionian DEFGABCD - Dorian EFGABCDE - Phrygian FGABCDEF - Lydian GABCDEFG - Mixolydian ABCDEFGA - Aeolian BCDEFGAB - Locrian If your chord progression is CFG you can solo over the chords using these scales: C Dorian, F Lydian, and G Mixolydian. That's when the modes become useful. Mastering this concept should be paramount to a lead guitarist.
    So play the C major scale but call it three different names just for the hell of it. That doesn't sound like a useful concept to me.
    Let me put it like this, When you play an Am scale aren't you also playing a C major scale just calling it something different? Theoretically it's still a C major but you're mind in honing in on the Am scale. Try to do that with all the modes (scales) when you play over your chord progression. I'm no music teacher, just trying to share some knowledge.
    I tend to think not, because you are resolving to A if you are playing A minor. Not the C. That's why it's the same notes but different sound. When you play a G major chord you don't refer to it as a derivative of a D(Stupid extension here) chord? Because of the focus of the notes you are playing. If you are playing E Phrygian, it is just that. Not the 3rd mode of C major, because then you are going to think in C and it loses all of it's own identity.
    steven seagull
    It all depends on the context - the backing chords will define what scale a collection of notes will fall in, not the intentions of the player.
    Would you be able to create some examples for us? Help us turn theory into music.
    Great article Chris! I totally agree with this approach and thank you for sharing it, however I noticed a few mistakes: 1.The Simpsons Theme was composed by Danny Elfman (not Hams Zimmer!) 2. In the examples above, you show both tabs and notation, but the notation has some enharmonic errors. Thanks!
    I noticed those too. Gpro seems to default to calling any accidental by its sharp name unless you input the key signature so both times you see A# in the lesson they should be read as Bb. Great intro to modes, Chris!
    Amazing - I thought it was a well-written, clear article, but I've learned so much more reading the comments! So if I understand, even if I play C's Phrygian mode (DEFGABC) over a C chord, it'll still sound like a C major scale because I'm just playing the notes of C over a C. But if play the same scale over an Dm chord, it'll give me the Phrygian scale's flavour? So if someone plays a C major-based progression, and I just play C major scales over it, I'll be accidentally swapping modes with each chord, whereas if I modified my scales to match the modal scales, I can keep the flavour I'm aiming for?
    If you have a progression in C major, and you play the notes of C major over it, it will be C major. Nothing modal about that.
    A modal use of C Ionian might be to use the C Ionian scale over an F Major Chord Progression. It would create tension any time you were playing any chord with the Bd in it. This isn't necessarily a textbook example of modal playing within Ionian modes. But, I disagree with your premise that there is "nothing modal" about it. It is just that it is the most common "mode" used in Western music so it gets ignored as "just the major scale" the same way Aeolian becomes "just the Minor scale".
    That's a good lesson! +1. One thing though, the simpsons theme is in lydian flat 7 (a mode from the harmonic minor scale).
    Sweet child o mine is not using a G ionian scale Its in D major.
    Chris Zoupa
    There's no C# so it's D mixolydian.
    The C is borrowed from the relative minor. Unfortunately most of your song examples are not modal they just use non-diatonic chords.
    It's a D Mixolydian (or Db if you tune down the guitar to Eb). It's a fair argument that the C chord may come from the parallel minor, but it's not just the chords. Listen to the lead guitar solos, the bass intro etc... if anything, the A chord at the chorus is the one borrowed from the Ionian / Major scale so we'll have a dominant 5th chord. I doubt Slash or Axel knew any of that....
    Sweet Child of Mine does not resolve to a D7 chord, it resolves to a D major chord. This is why it is not in D mixolydian. As you noted the chorus also has an A chord, creating a V - I cadence. This cadence ensures that the song is is in a key, not a mode. Modes cannot borrow chords, they are extremely limited in their use. As for the lead guitar solos, there's a clear modulation to Em for those, and the verse licks never emphasise the b7 so they don't sound mixolydian at all.
    It isn't a requirement of a mixolydian key to resolve to a 7 chord. The fact that there is a V - I cadence means naught as well. If a song were in lydian (raised 4th) the I chord and V chords remain unchanged (relative to a straight major key; both major chords with a dom 7 on the V if you so choose). Therefore, a V-I cadence in lydian is equivalent to a V-I cadence in dorian. If the song was based in a mixolydian scale, the difference (if you strictly follow the mode) is merely the dominant chord would be a minor chord rather than a major - not an authenric cadence but still a cadence - which doesn't have to (but can) resolve to a 7 chord.
    You actually do have to resolve to a D7 chord. If your song resolves to D major, you are in the D major key. The issue is that it's really hard to create a song with more than two chords that resolves to a chord other than a major or minor chords. Also if I was confronted with a song that had a major I and a minor v, I would suggest that I am analysing the song incorrectly.
    You don't have to resolve to a D7 chord. This is not what makes something modal.
    When it comes to harmony, the fact that you are resolving anything at all makes the argument of this song not being modal. A defining characteristic of modal music of any genre is that the harmony for all practical purposes is static. Even when you have chords that are not the 1 chord, their notes are built from the same scale as the 1 chord. As far as melodies are concerned, especially modal melodies, there almost isn't a more revealing quality of the key of a melody than the note it ends on. Blues progressions have tonic 7 chords. Never have I ever heard someone say "we're playing a blues in D mixolydian" because songs in D mixolydian will follow modal music characteristics, meaning static harmony and a melody that uses mostly but likely only diatonic notes. Neither the blues, nor this song follow those rules. The song is in D and has a major 3rd. If I had to give a quality I would say the song is in D major. Whether they play with the 7th is basically irrelevant.
    It's the defining feature of the mixolydian mode. What would you say makes something modal?
    Argh I mean the C is borrowed from the PARALLEL minor. Rookie error.
    I'm reading the discussion below (*edit: above) and am surprised by the confusion. Sweet Child resolves to the D major chord so clearly D is it's tonal center. It MAINLY uses C natural instead of C# so it's D mixolydian. Period.Modes, including the major and natural minor scales (Ionian and Aeolian as Chris shows in his excellent lesson) are simply the set of notes within the melodies and harmony (chords) of any song.Other mixolydian examples: Taking Care Of Business by BTO and Sweet Home Alabama by Lynard Skynard
    You cannot simply harmonse the notes of the mixolydian scale and expect a modal song to pop out the other side. They don't work like that mate.
    You clearly have a strong opinion about the definition of modes as seen in you're multiple posts disagreeing with this lesson and it's definitions. I'm not gonna argue with you, mate. For those of you who are confused, the tonal center of sweet child is clearly D and the set of notes used are D E F# G A B C and include C# in the chorus. What Chris was showing is that the b7th degree in the defining first progression is a great exaMple of what the mixolydian mode sounds like.
    nothing like posting a reply from a phone and getting autocorrect grammatical errors and weird use of caps in the middle of words
    Yeah these things happen, no worries dude. I really think that assuming that simply because a non-diatonic chord is employed at some point means that a song is automatically "modal" just ignores the freedom that keys grant, or otherwise does not illustrate an understanding of how keys work. Keys were developed to address this specific situation, to include non-diatonic chords and notes within the same harmonic context during a song. The modal system could not accomodate for these situations.
    Just the opposite, dude. Modes help define why a specific non major or non minor tone works so well consistently through the harmonies and melodies of a piece. Music is way simpler than thinking of modes as belonging to free form expression. You, my friend, are more interested in arguing an archaic viewpoint than using your ears. Listen, bro. I'm donetalking with you on the subject.
    Oh I'm happy to say "you fan use the mixo scale over a bVII in a major key", that's fine, I'm just not going to immediately assume that the song is modal just because the song has a bVII.
    The chorus has both C's and C#'s. And technically it's a half step down so Db would be the key :p
    Modes = pieces of the Major scale they were derived from. So you can learn them as 84 separate scales and the theory to go with it. Or: Learn the 12 major scales and the theory behind them. Your choice. Doesn't matter if you want to call an A minor scale "Aeolian", "natural minor" or "RELATIVE MINOR" <--- because they are all just the C major scale over an A minor chord/vamp/progression derived for the harmonized C major scale. Yes the name and sound is different but the theory is the same and is a LOT easier to remember and master.
    blazing riff
    Very interesting point guys. I'm a strong believer that music theory is a big thing in when it comes too musical developement. However, I think there is way too much stress on modes. Yes, they all have a typical colour but when I turn on my radio I just don't hear ANY piece of music that is modal. Modes are a certainly an interesting topic (It's nice to bust out some modal licks over a vamp) but it's not the holy grail in becoming a better musician.
    Actually you would be surprised how many songs are in modal keys.Phrygian and Mixolydian are two of the most used modes in metal and rock music.Dorian is basically used as the default minor scale in Jazz music.Steve Vai uses lot's of Lydian.Satriani uses well,everything . Maybe they are not important for your playing,and I'll say play whatever you feel is right.But I think that when you start understanding their differences and recognising their own sound and character,it gives you a whole new perpective when listening to music.It makes music so much more fun to listen to.
    blazing riff
    I agree that it's nice to be recognize modes in a piece of music. I'm just trying to drive the point that there is (in my opinion) too much stress on modes. Like everybody keeps talking about the Sweet child of Mine solo being in mixolydian. If you look at the collection of notes: yes it's mixolydian. However the chords in the song just resolve to the I-chord which makes it a diatonic progression. Is this modal, no.
    Actually the solo is in E Minor,the intro is in D mixolydian and I believe the verse and the chorus are too. Anyway,the point in modes is that you can easily move between them in a song to change the mood.If you feel they are not that important that's ok.Slash didn't give a **** if the intro in Sweet child of mine was in mixolydian or the solo was in E minor.He played what sounded good to himself. Personally,they helped me alot in understanding music better and become a better musician.
    But it's not in D mixolydian. It simply uses a non-diatonic chord.
    Hmmmm the intro has only C's and a D/C/G chord progression which is very mixolydian like.The chorus has an A major and a chord progression tha leads to D.The C on the intro is definitelly borrowed from D mixolydian.I would say that the intro is in D mixolydian the chorus in D major and the solo in E minor. Anyway,Ionian and Mixolydian are two very closly related keys.You can change between them pretty easily.I think there is no point to argue.
    The C is borrowed from the parallel minor. The mistake you're making is assuming that the tonality of a mode can simply be created through harmonising the notes of it's associated scale. Unfortunately not. It has to resolve to D7 to be mixolydian, not D. D, C, G is not mixolydian. Try out this instead: D7 - C9/D x forever. That'll get you a D mixo song, provided you don't employ any other chords.
    Why does it have to be D7? I get that C is the 7th but why is it needed to create a mixolydian song? Satriani's Summer Song is in A Mixolydian and it uses an A5 - GM7/A chord progression.(Well not the whole song is in mixolydian,part of the main melody is.)
    Although Satriani mayn't play the 7, it's implied. 5th chords almost always have implied notes. As for "why" it needs to resolve to a D7, the answer is easy. If it resolved to D major, the key would be D major. You want mixo, which has a harmonic basis of 1, 3, 5 and 7, so it needs to resolve to a chord containing all these notes. If you try it out, it's not an easy feat to do. Keys were developed around 200 years ago so that more freedom can be employed at least from an analytic standpoint for songs.
    Ok I get it.I thought that playing D/C foverever would be enough to create a mixolydian sound. But back to sweet child of mine.Couldn't you say that he uses D mixolydian to solo over D major?You know,in order to use C as an accidental.It would also make more sense since both Mixolydian and Ionian are Major keys.I mean D Dorian has a C too as well as D Aeolian from which you say it borrows the C chord.But since they are both Minor keys wouldn't it make more sense to borrow that C from a Major key?
    blazing riff
    With the risk of coming off like a douch, I think you just need a firmer understanding in harmonising scales and parallel minor. Like AlanHB said: he uses a none-diatonic chord. He isn't using mixolydian (yes it contains the intervals of a mixolydian scale). In the case of sweet child of mine the intervals he uses should be looked at as accidentals to add flavour.