Chord Progression

[xerox02]

Hello everyone

I am new here, and I had a few quick questions.
When you do a chord progression, must you always start on the root chord of the key you are doing it in?

Let's say I was in C Major, would I always have to start on C Major for a chord progression?

If you don't always start on C Major, how can you tell the difference if you are in A minor or C major when all the notes are the same?

How would it be possible for people to know what key your in with out looking at your sheet music?

On a side note, I am very interested in learning the basics of jazz improvisation, I know all the Major, Minor, and Blues scales, and I use 7th, 9th and 11th chords, but I am not sure where to go from there. I always improvise for fun with the scales, but I have a hard time modulating to into new keys.

Thanks a lot!

[Malcolm]

Hello everyone I am new here, and I had a few quick questions.
When you do a chord progression, must you always start on the root chord of the key you are doing it in? Let's say I was in C Major, would I always have to start on C Major for a chord progression?

No you do not have to start with the I chord. Now your verse should end with the I chord. Why? Each verse is a complete thought. A verse starts a thought, discusses it, reaches a climax and then closes this thought. Returning to the I chord brings resolution and returns the verse to rest -- so a new thought can be started in verse number two.

If you don't always start on C Major, how can you tell the difference if you are in A minor or C major when all the notes are the same?

Lets take this one more step Am and C (major) not only have the same notes they also have the same chords. Three major chords, C, F & G and three minor chords, Am, Dm & Em with one diminished chord Bdim. So how do you tell if it's in C or Am? Look at the chords used. If the song is using the major chords, C F & G you are in a major key aka C. If the chords used were the three minor chords, Am, Dm & Em your song is in the key of Am. Long story short - look at the chords being used. OK that's fine but if I had a ii, V, I progression in C then I would have Dm, G, C. What now? Good question. Look for the V I cadence G, C is the V I cadence in this case and points us to the key of C.

How would it be possible for people to know what key your in with out looking at your sheet music?

Couple of ways. Someone tells you this song is in G or C or whatever, or you listen and make that decision yourself. Not a big deal --- Listen to the song and sound your E string one fret at a time. When what you are hearing from the song and what you are doing on the E string come together - sound good together - you've found the tonal center, thus the key. Look down and see what note this happened on - that's your key. First step in jamming to your CD's.

On a side note, I am very interested in learning the basics of jazz improvisation, I know all the Major, Minor, and Blues scales, and I use 7th, 9th and 11th chords, but I am not sure where to go from there. I always improvise for fun with the scales, but I have a hard time modulating to into new keys.
Thanks a lot!

Let's forget about modulating to a new key, let's just worry with improvising in one key. Improvising is playing melody. If you are relying upon scales, major 7 or pentatonic 5 or modes and running them in scale order they sound like a scale exercise. To break away from that you have to start thinking melodic phrases. I think pentatonic scales do this the best. Why? The pentatonic scale will give you three chord tones and two safe passing notes to build you melodic phrase from. Much easier than having to gather some good sounding licks from 7 notes, IMHO. Should mention here the secret to harmonizing a melody line is for the melody and the chord's to share some of the same notes. When do we need to change chords in a song? When the melody moves on to notes not found in the old chord. When this happens we go out of harmony and have to find another chord that does contain some of the new melody notes. Now if you did not already know that I just opened a whole new World for you. It's always a good idea to gather your melodic phrases from the chord tones. Back to what I said about pentatonic scales. There are some great articles on this site see what they have to say about pentatonic scales. http://www.ibreathemusic.com/article/90 At the end of each article there will be a link to the rest of the story - be sure and go to this link.

Good luck.

[xerox02]

Thank you so much man! This was very enlightening for me. I am
actually a experimental electronic producer ( I am alright, lol ), but I do other stuff. Once I get home I'll give a more proper reply. )))).

For jazz, what are the common scales used, blues, pentatonic, the different modes like lyodian and etc?
From what I know using the circle of fifths or relative keys are good for changing keys.

[Malcolm]

For jazz, what are the common scales used, blues, pentatonic, the different modes like lyodian and etc?
From what I know using the circle of fifths or relative keys are good for changing keys.

Jazz is going to be in the keys the horns like, i.e. the flat keys, so the keys may be something you are not used to using. http://www.ralphpatt.com/Song.html Notice the backing track button.

Standards will be written out for you so that eliminates one problem. Improvising I suggest you use the mode that produces the mood you want.
Ionian = 1, 2, 3, 4, 5, 6, 7 and gives an attractive up beat feeling
Lydian = sharp the 4th and get a simular major sound, some say dreamy sound.
Mixolydian = flat the 7th and get a Latin - I hear Mexican - South of the border sound. Then of course used over blues dominant seventh chords.

Aeolian = 1, 2, b3, 4, 5, b6, b7 and gives a sad mood.
Dorian = sharp the b6 back to a natural 6 for an attractive jazz minor sound.
Phrygian = flat the 2 for an exotic Spanish, some say Middle Eastern sound.
Locrian = keep the flat 2 and add a flat 5 for a dark and tense sound.

None of that works without the modal vamp droning in the background. Modal vamps sustain the modal mood, chord progressions sustain the tonal center of the scale - which may have nothing to do with the mood you want.

Going to another key in the same song. Find a shared chord. Go to it and take off from there. You've set a mood sure you want to move to another?

You may find "back cycling" interesting. http://www.ibreathemusic.com/forums/...hp/t-8383.html

[JonR]

When you do a chord progression, must you always start on the root chord of the key you are doing it in?

No.
It's common, as a way of establishing the key to start with - especially in pop and rock music (a little less often in jazz). But it's much more common (and important) to end the song with the tonic. ("Tonic" is the right name for the "root" chord of a key.)
Ending with the tonic makes the song sound complete.
Which is not to say composers don't sometimes want to end a song on an incomplete sound...
You know the way you can sometimes just let a sentence tail off without bringing it to a...

If you don't always start on C Major, how can you tell the difference if you are in A minor or C major when all the notes are the same?

A tune in the key of A minor will generally feature Am at the end and (probably) the start of the song.
It will also very likely feature an E major chord somewhere, which helps you hear A as the tonic note, instead of C.

How would it be possible for people to know what key your in with out looking at your sheet music?

Listen. It's usually pretty easy to pick up the tonic by listening for where a chord sequence seems to come to rest - the point at which you could end the song comfortably without it sounding unfinished.
(Of course the tonic chord will occur many times before the end of a song, so it will often seem short to end on an earlier one. But harmonically it will sound OK. Like the period at the end of a sentence or paragraph, instead of at the end of a chapter.)

On a side note, I am very interested in learning the basics of jazz improvisation, I know all the Major, Minor, and Blues scales, and I use 7th, 9th and 11th chords, but I am not sure where to go from there. I always improvise for fun with the scales, but I have a hard time modulating to into new keys.

Study fake books - or better, the well-known "Real Books": collections of jazz standards of all eras.

"Modulating to new keys" is something you (might) do when composing a new tune.
When improvising, you simply follow what the chords tell you: if they modulate, then you do. If they don't, you don't.
(Jazz improvisers can still play "outside" the current harmony, for contrast and drama, but they never play in a different key.)

For any tune you want to improvise on, the first thing you should do is learn to play the melody. Then study the chords, and identify the key (or keys) and chord functions - the "job" each chord is doing in the sequence.

[JonR]

For jazz, what are the common scales used, blues, pentatonic, the different modes like lyodian and etc?

For all jazz pre-1959 (and much after): major and minor keys. No modes at all. Plenty of blues tho!

As Malcolm says, the most common keys in jazz tend to be those that are easy for horns, such as F, Bb, Eb and Ab, and their relative minors (Dm, Gm, Cm, Fm).
(Just as rock songs tend to be in easy keys for guitar, like G, D, A or E.)

In post-1959 jazz (following Miles Davis's "Kind of Blue" album) you will hear a lot of "modal" harmony. This means tunes based on long sequences on one chord, or (more likely) strings of chords that seem to share no single key relationship. The chords in this kind of jazz are often "quartal" - built in 4ths instead of 3rds. This type of jazz tends to sound more "moody", "fluid" or "impressionistic" - it has grooves or drones, in place of the snappy swing or sweet ballads of older jazz.
A lot of the time, modern jazz will combine the old key-based habits (functional chord progressions) with newer modal ones in the same tune.

From what I know using the circle of fifths or relative keys are good for changing keys.

True. The circle of 5ths is also useful within any one key, for understanding how chords move. (as in the "backcycling" Malcolm mentioned.)
Again, you will learn the most by analysing chord sequences from jazz standards.

[xerox02]

Wow man, you guys are seriously blowing mind (I am completely serious).
I have class at 8:15 pm, but once it's over I'll make a full reply.
Thank you so much! This is a great forum.

Old Stuff: http://www.archive.org/details/TrialsAndErrors (mix of my my old stuff, but I like my old stuff better)
New Stuff: http://soundcloud.com/riseorfail

[Malcolm]

If you do not have this http://www.jazzwise.com/catalog/arti...articles_id=10 help yourself, it's a must have.

[xerox02]

Let us say that in a chord progression of C major, you end in a Inversion chord of C major, or a substitute chord of c major. Does that also bring the sound home (aka cadence)?
Also, with all the scales that are available, how do you go choosing one when you compose?
Do composers think of music first, and then find out what scale the music in their mind is? Or do they use the scale to guide them?
The greek scales, and the explanation you gave for each one is awesome. I wonder how this was established, and why aren't there any new scales today?
I never hear about people producing in the greek modes, but they seem really great, because they can achieve a specific kind of mood, which isn't as broad as Minor (sad) and Major (happy). Jap in sen (Japanese sounding) or Blues (Blue sounding)
It is very interesting that old jazz was all in Major, Minor and Blues. It's great to see how it has expanded since then. Do any of guys know the pianist Hiromi?
I've been trying to work on my relative pitch by understanding, and memorizing intervals. I want to learn how to compose better, and more important get the melodies and harmonies out of my head easier, without worrying too much about technical stuff.

Thanks again guys, I have a lot to study with what you've given me, and I am definitely going to be coming back to this thread regularly.
Later on, I can put some of my music on here hopefully .

[JonR]

Let us say that in a chord progression of C major, you end in a Inversion chord of C major, or a substitute chord of c major. Does that also bring the sound home (aka cadence)?

No, not entirely.
Best thing is to try it out and see what you think.
Generally, you need a C on the bottom of the final chord for any kind of firm closure (in key of C, that is ).
But if the C is in the bass, you can often have a mix of extensions on top, and the melody needn't finish on C. (It's common for jazz singers to find an alternative final note, such as the 3rd, maj7 or 9.)

But - as I said before - there is no rule (at least in modern music) that says every tune needs a firm closure (perfect cadence). You simply need to try out the alternatives and listen.

Also, with all the scales that are available, how do you go choosing one when you compose?
Do composers think of music first, and then find out what scale the music in their mind is? Or do they use the scale to guide them?

Pretty much the former, most of the time.
Sometimes I begin with an interesting chord, or a short melodic phrase, sung or hummed, that I've found just by messing around. I work from that, developing it by ear as much as I can, trying to ignore the theory that suggests itself. (This is because one never knows ALL the theory of music - there's always something that will sound good for some reason you don't know. So you have to let your ear guide you.)

Occasionally I might start with a "project" in mind - eg to compose in a specific mode, or a specific unusual scale of some kind. But that's rare (and doesn't often produce good music). If it works, it will be because the ear takes over in the end anyway and runs the show.

Most of my own music is key-based, with conventional chord sequences (probably because that's what I grew up with), but I do try and use surprising chord and key changes when I can, to keep it fresh. If I use modal ideas, it will usually be in combination with functional ones.

The greek scales, and the explanation you gave for each one is awesome. I wonder how this was established, and why aren't there any new scales today?

Basically - if it ain't broke, don't fix it!
However, while the core scales and modes of our system have remained pretty much unchanged for centuries, they have been adapted over the years, as musical fashions change.

(Brief and no doubt contentious history lesson follows...)

Around 1500 years ago, European church authorities standardised (and re-arranged) the Greek modal system into 4 basic modes - dorian, phrygian, lydian, mixolydian. It was felt they were the most ideal for their musical purposes - either for their sound, or their mathematical organisation or (more likely) both.
Around 1000 years after that, Ionian and Aeolian were officially added to the list (although Ionian had been in use in folk music for some time before).
It was actually a very slow process of modification and tweaking, beginning with the "white notes" only (ABCDEFG), gradually accepting accidentals (starting with Bb and F#), before our modern system of 12 KEYS (based on Ionian and Aeolian) took over around 400 years ago (very approximately).
The "major-minor key system" (aka the "common practice period" or CPP) ruled for 2 or 3 centuries, and produced all the great works of the baroque, classical and romantic eras - as well as practically all the western popular music of the 20th century.

The reason for this focus on just two of the ancient modes was the way they enabled HARMONY to develop.
A special property of Ionian mode is what happens when you harmonise it in 3rds. You get TONALITY - the sense of a strong keynote, a gravitational centre for the music. Harmonising the notes ABCDEFG in 3rds always points most strongly to a C major tonic, whatever mode you think you're starting in.
There are physical acoustic reasons for this, but also cultural ones, in that the "natural" aspects of Ionian have been hammered into our brains over the last 300 years or so, so it feels even more natural than it is (which is actually not very much).
Aeolian mode then became the "sidekick" of Ionian, a necessary "minor" contrast to Ionian's major. But it was still adapted to operate like Ionian, by altering it to harmonic or melodic minor to increase the gravitational pull of the tonic.

IOW, the scales of western music were deliberately limited because harmony was the main show in town. European classical music is (was) unique in the history of world music in its development of harmonic sophistication; but that necessitated the use of simple scales and fixed pitches (the machine won't work if you start messing with the cogs...) Other musical cultures have rudimentary harmony (or more likely none), but are much more sophisticated in melody, rhythm and timbre. (That's why there are 100s, 1000s of "ethnic" scales, but a mere handful of western ones.)

Something interesting happened around 100 years ago, when classical composers began to feel the CPP system was worn out. (The trouble with harmony is it operates with dissonance and consonance as contrast. It's a bit like a drug, in that our ears (over years or generations) can develop a tolerance to dissonance, so we need more and more in order for the music to work, to remain exciting. Eventually we run out of dissonances that are strong or surprising enough...)
New experiments were tried, with atonalism (Schoenberg), revisiting old modal ideas to create impressionist music (Debussy, Ravel, Satie), polytonalism (more than one key at once), and various later avant garde modernism (Stockhausen, Cage, etc).
Most of this music had little or no appeal to the general public - who are still addicted to tonality (and probably always will be).
In jazz, a very similar process occurred in the 1960s, as musicians began experimenting beyond the old key system, using modes, free jazz (improv totally from scratch), and toying with ideas from rock music (fusion). Again, this clearing of the decks tended to leave the public behind (with the notable exception of Miles's first experiments on "Kind of Blue", the biggest selling jazz album of all time.)

Rock music was an offshoot of black popular music, of course, driven by blues - itself a form of folk music, with modal aspects. The one characteristic of modal music that rock and pop fans appreciate is the "one-chord groove" - which is great for dance music, or hypnotic "trance" sounds. A lot of rock bands therefore gravitate to modal sounds without knowing (or caring) about the theory at all.
Of course, if you only have one chord (or less, one bass note or drone), then your scale options are freed up. You can introduce ethnic style decoration and ornamentation. You can play with rhythmic ideas. Hence the increased appeal (over the last 50 years) of ethnic folk music of all kinds, and its influence on rock and jazz.
(Meanwhile, of course, cultures like China have fallen in love with the equally alien - to them - sounds of european classical music...)

I never hear about people producing in the greek modes, but they seem really great, because they can achieve a specific kind of mood, which isn't as broad as Minor (sad) and Major (happy). Jap in sen (Japanese sounding) or Blues (Blue sounding)

This is because the kind of moods evoked by types of scale are very subtle. In the west we are used to the much broader (and cruder) range of moods available from the harmonies of the major and minor keys, and also from simple changes in tempo or orchestration.
Take a minor key tune and play it fast, it won't sound "sad" any more. Play a major key tune slow, it probably will. That's how little effect even our major and minor scales have - never mind the more subtle sounds of the modes.

Our major-minor key system (at its best) is like an "emotional roller-coaster". A modal piece, in comparison, is a single mood, something contemplative and rarely obvious. It doesn't yell at you, piling on singalong hooks like key-based music does - you have to go to meet it, give it space and time, get into the vibe.

Indian raga music is modal music par excellence. They really understand the subtleties of mood each scale evokes - or rather is supposed to. We in the west would be hard pushed to identify an "evening" raga from an "afternoon" one - but I suspect even for Indians those associations are culturally learned as much as our key ones are.
But ragas underline how sophisticated music can be when it uses no harmony, no chords at all. So does much African drum music - which may not even have pitched sounds, just incredibly detailed interactions of rhythmic pattern.
(Adding chords to a raga would be really silly. Like putting wheels on a horse...)

I've been trying to work on my relative pitch by understanding, and memorizing intervals. I want to learn how to compose better, and more important get the melodies and harmonies out of my head easier, without worrying too much about technical stuff.

Good plan.
But still, don't do too many pure exercises, out of the context of real music. Keep listening to actual music, paying attention, and trying to hear everything that's going on in it. Not just chord changes and intervals, but kinds of instrument, studio effects, rhythm patterns, etc.
The more different kinds of music you listen to, the more "original" your own music will be.

[xerox02]

awesome, I found this awesome spanish guitar piece:
http://www.youtube.com/watch?v=dQxHQ...layer_embedded
I am a huge fan of bossa nova!
I wonder what key this is in, is it Mixolydian?
I'll make a more extensive reply later, thanks!

[JonR]

awesome, I found this awesome spanish guitar piece:
http://www.youtube.com/watch?v=dQxHQ...layer_embedded
I am a huge fan of bossa nova!
I wonder what key this is in, is it Mixolydian?

That's not bossa nova, more like classical Spanish, with flamenco touches.
It's mostly in a minor key, with hints of phrygian, but there's quite a lot of modulation. (I haven't worked any of it out, just played along with sections of it.)
No mixolydian as far as I can tell. (And mixolydian isn't a "key" anyway, strictly speaking. )

If you want bossa nova guitar, try this:
http://www.youtube.com/watch?v=Rq8Zq...eature=related
Bossa nova (literally "new groove", or "new thing" - well, it was new in 1958...) is really a rhythm (a repeated 2-bar motif); not associated with particular scales or modes, but usually in a major key, sometimes minor. Harmonically characterised by quite rich chord types and changes.

[xerox02]

That's not bossa nova, more like classical Spanish, with flamenco touches.
It's mostly in a minor key, with hints of phrygian, but there's quite a lot of modulation. (I haven't worked any of it out, just played along with sections of it.)
No mixolydian as far as I can tell. (And mixolydian isn't a "key" anyway, strictly speaking. )

If you want bossa nova guitar, try this:
http://www.youtube.com/watch?v=Rq8Zq...eature=related
Bossa nova (literally "new groove", or "new thing" - well, it was new in 1958...) is really a rhythm (a repeated 2-bar motif); not associated with particular scales or modes, but usually in a major key, sometimes minor. Harmonically characterised by quite rich chord types and changes.

haha kool, do you use the modes with other scales? How do you use the modes work?

[JonR]

haha kool, do you use the modes with other scales? How do you use the modes work?

It's best to consider keys and modes separately.
In a sense, our major and minor keys are examples of just two very specific modes (Ionian and Aeolian-with-alterations, as I said).
You don't use the other modes "with" these two. The other modes are totally separate ways of making (composing) music.

However, in rock music, you do often get what seem like mixtures of the two ways of thinking (key or mode). Very few rock musicians know or care about the theoretical niceties, after all - they just go for sounds they like, learned from their influences.
You typically have major key sequences - to start with - but altered or coloured in some way that could be described (not entirely correctly) as modal. IOW, rock bands treat the major key as something that can freely be altered (usually by flattening some of its steps to make it bluesier, funkier or heavier), just as a minor key (traditionally) can have its 6th and 7th raised.

Take G'n'R's "Sweet Child o' Mine", a very typical rock song. The verse is "in D major" (tuned down half-step), in that the keynote is clearly D. But there is no A chord, and there's a C instead. (basic sequence: D-C-G-D)
So - this is not the "D major key", strictly speaking: because it has a b7 note and bVII chord. We could describe it as "D mixolydian mode".
However, the chorus does contain an A major chord, the usual V of D major. So that part is clearly "D major key".
Overall, I guess you could call it "mixolydian major" - major key but with the significant addition of a bVII chord (along with a normal V chord).
You can also describe it as "major key", but with a bVII chord "borrowed from the parallel minor" (because C major comes from the D minor key). "Modal interchange" is another term for this kind of "cross-pollination" of keys and modes.
IOW, there are a few ways a theorist might describe what these guys are doing - while the band themselves could hardly give a damn!

This is an extremely common combination in rock music - you hear it in a lot of Beatles songs too: mixolydian verse, major key chorus. In fact, mixolydian mode was one of Lennon's and Harrison's favourite sounds (tho they didn't know it had a name). McCartney preferred major and minor key sequences.
Eg "Hard Days Night" - G mixolydian verse (with classic G mix opening chord), G major key chorus and bridge
"Norwegian Wood" - E mixolydian verse, moving to E dorian, and lastly to an E major key (Ionian) ii-V. (Classic example of "modal interchange".)
"I Feel Fine" - mixolydian riffs, in the context of a bluesy G major key for the verse. The bridge is straight (non-bluesy) G major key.
"Day Tripper" - E mixolydian vamp and riff. (This tune, in fact, is an intriguing mix of dom7 chords, many not related to the E major key.)
"If I Needed Someone" - A mixolydian - bridge (unusually) in B minor.
"She Said She Said" - Bb mixolydian right through.
"Tomorrow Never Knows" - C mixolydian right through.
"Within You Without You" - C# mixolydian (classic standard sitar mode) almost right through (hint of dorian in the bridge).

The Beatles attraction to - and take on - mixolydian was a kind of mix of bluesy b7s and Indian drones. Reflecting their influences, of course.

The Stones also use mixolydian, but in a much more blues-based way that was to become staple in mainstream rock. Eg:
"Sympathy for the Devil" - v. similar to Sweet Child o Mine, in its D mixolydian verse (D-C-G-D) and D major key chorus.
"Satisfaction" - E mixolydian riff, verse and chorus; E major key pre-chorus ("I tried, and I tried...")
"The Last Time" - E mixolydian right through. Or - arguably - E mixolydian verse and A major key chorus.

In short, any time you get a major key with a bVII chord (eg D in key of E, or G in key of A) you have a kind of mixolydian vibe - esp if you don't have a major V chord.

Dorian mode is probably the next most common modal sound in rock (but not nearly as common as mixolydian, nor as common as normal major and minor key). From one angle, it's simply a minor version of mixolydian: mixolydian with a b3.
From another, it's a minor key scale, but with a major 6 degree - and with no raised 7th alteration (as in harmonic or melodic minor).

The archetypal example is "Oye Como Va" by Santana, which is totally A dorian. (Because it's a Cuban tune, and dorian mode is widespread in Cuban music.)
The verse of Van Morrison's "Moondance" is also classic A dorian mode, but it moves to the A minor key in the prechorus.
The other classic rock example is the solo section of the Doors "Light My Fire", in A dorian.
Pink Floyd's "Breathe" has a lengthy E dorian intro and verse, but then moves into a mix of E aeolian ("long you live") and E phrygian ("all you touch..")

Deep Purple's "Smoke on the Water" is a kind of bluesy G phrygian riff and verse, with a G dorian IV chord (C major) in the chorus. (IOW, they combine all kinds of minor scale sounds - phrygian, dorian, blues, aeolian, even a hint of locrian - without caring too much! )


The whole point here, remember, is to identify what scales or modes a song consists of, by analysis. Modes are a system of terminology to aid our description of what's going on music. (Although keys and modes are two different things, modal terms can sometimes help in describing the way rock musicians adapt major and minor keys.)
There is a widespread and mistaken idea that modes are some kind of alternative "moods" that you can "apply" to an existing tune when improvising. This is not the case.
A related confusion is to assume you need to think about the "relative" modes in a major key (the other modes of the same scale). Eg, to treat a Dm chord in the key of C as "D dorian". This is strictly correct in one sense, but is not musically useful, is a waste of time, and can be misleading.

[xerox02]

It's best to consider keys and modes separately.
In a sense, our major and minor keys are examples of just two very specific modes (Ionian and Aeolian-with-alterations, as I said).
You don't use the other modes "with" these two. The other modes are totally separate ways of making (composing) music.

However, in rock music, you do often get what seem like mixtures of the two ways of thinking (key or mode). Very few rock musicians know or care about the theoretical niceties, after all - they just go for sounds they like, learned from their influences.
You typically have major key sequences - to start with - but altered or coloured in some way that could be described (not entirely correctly) as modal. IOW, rock bands treat the major key as something that can freely be altered (usually by flattening some of its steps to make it bluesier, funkier or heavier), just as a minor key (traditionally) can have its 6th and 7th raised.

Take G'n'R's "Sweet Child o' Mine", a very typical rock song. The verse is "in D major" (tuned down half-step), in that the keynote is clearly D. But there is no A chord, and there's a C instead. (basic sequence: D-C-G-D)
So - this is not the "D major key", strictly speaking: because it has a b7 note and bVII chord. We could describe it as "D mixolydian mode".
However, the chorus does contain an A major chord, the usual V of D major. So that part is clearly "D major key".
Overall, I guess you could call it "mixolydian major" - major key but with the significant addition of a bVII chord (along with a normal V chord).
You can also describe it as "major key", but with a bVII chord "borrowed from the parallel minor" (because C major comes from the D minor key). "Modal interchange" is another term for this kind of "cross-pollination" of keys and modes.
IOW, there are a few ways a theorist might describe what these guys are doing - while the band themselves could hardly give a damn!

This is an extremely common combination in rock music - you hear it in a lot of Beatles songs too: mixolydian verse, major key chorus. In fact, mixolydian mode was one of Lennon's and Harrison's favourite sounds (tho they didn't know it had a name). McCartney preferred major and minor key sequences.
Eg "Hard Days Night" - G mixolydian verse (with classic G mix opening chord), G major key chorus and bridge
"Norwegian Wood" - E mixolydian verse, moving to E dorian, and lastly to an E major key (Ionian) ii-V. (Classic example of "modal interchange".)
"I Feel Fine" - mixolydian riffs, in the context of a bluesy G major key for the verse. The bridge is straight (non-bluesy) G major key.
"Day Tripper" - E mixolydian vamp and riff. (This tune, in fact, is an intriguing mix of dom7 chords, many not related to the E major key.)
"If I Needed Someone" - A mixolydian - bridge (unusually) in B minor.
"She Said She Said" - Bb mixolydian right through.
"Tomorrow Never Knows" - C mixolydian right through.
"Within You Without You" - C# mixolydian (classic standard sitar mode) almost right through (hint of dorian in the bridge).

The Beatles attraction to - and take on - mixolydian was a kind of mix of bluesy b7s and Indian drones. Reflecting their influences, of course.

The Stones also use mixolydian, but in a much more blues-based way that was to become staple in mainstream rock. Eg:
"Sympathy for the Devil" - v. similar to Sweet Child o Mine, in its D mixolydian verse (D-C-G-D) and D major key chorus.
"Satisfaction" - E mixolydian riff, verse and chorus; E major key pre-chorus ("I tried, and I tried...")
"The Last Time" - E mixolydian right through. Or - arguably - E mixolydian verse and A major key chorus.

In short, any time you get a major key with a bVII chord (eg D in key of E, or G in key of A) you have a kind of mixolydian vibe - esp if you don't have a major V chord.

Dorian mode is probably the next most common modal sound in rock (but not nearly as common as mixolydian, nor as common as normal major and minor key). From one angle, it's simply a minor version of mixolydian: mixolydian with a b3.
From another, it's a minor key scale, but with a major 6 degree - and with no raised 7th alteration (as in harmonic or melodic minor).

The archetypal example is "Oye Como Va" by Santana, which is totally A dorian. (Because it's a Cuban tune, and dorian mode is widespread in Cuban music.)
The verse of Van Morrison's "Moondance" is also classic A dorian mode, but it moves to the A minor key in the prechorus.
The other classic rock example is the solo section of the Doors "Light My Fire", in A dorian.
Pink Floyd's "Breathe" has a lengthy E dorian intro and verse, but then moves into a mix of E aeolian ("long you live") and E phrygian ("all you touch..")

Deep Purple's "Smoke on the Water" is a kind of bluesy G phrygian riff and verse, with a G dorian IV chord (C major) in the chorus. (IOW, they combine all kinds of minor scale sounds - phrygian, dorian, blues, aeolian, even a hint of locrian - without caring too much! )


The whole point here, remember, is to identify what scales or modes a song consists of, by analysis. Modes are a system of terminology to aid our description of what's going on music. (Although keys and modes are two different things, modal terms can sometimes help in describing the way rock musicians adapt major and minor keys.)
There is a widespread and mistaken idea that modes are some kind of alternative "moods" that you can "apply" to an existing tune when improvising. This is not the case.
A related confusion is to assume you need to think about the "relative" modes in a major key (the other modes of the same scale). Eg, to treat a Dm chord in the key of C as "D dorian". This is strictly correct in one sense, but is not musically useful, is a waste of time, and can be misleading.

ah, hopefully I understand this correctly, but it is just a way for us describe certain kind of feels a music brings no matter what key it is in. So lets say its D Minor, but it gives kind of a jazzy minor feel for some reason, then we would say it's a D minor song with a Dorian feel.