Someone help me: what EXACTLY is the difference between a scale and a mode?

now consider playing the scale of C maj, but starting on a different note
e.g. C maj (one octave) D E F G A B C D

now this just looks like straightforward transposition, but consider the GAPS between each note

for Cmaj starting on C gaps are (in semitones) 2 2 1 2 2 2 1 (called an Ionian mode)
but Cmaj starting on D gaps are (in semitones) 2 1 2 2 2 1 2 (called a Dorian mode)

so starting on C if you play an Ionian Mode it would be C D E F G A B C
and starting on C if you play a Dorian Mode you'd play C D Eb F G A Bb C

you can apply the same trick for Cmaj starting on the other notes to get the tonal intervals for the other modes,
quickly then: starting on E = Phrygian, F = Lydian, G = Mixolydian, A = Aoelian, B = Locrian.

i'm going to go and lie down now, my head hurts.....

there are three ways to look at a mode. joni described two of them, the first being the mode as thea notes of a scale starting on any one of its degrees (1,2, ...7) its first degree is called the root. the Ionian mode is the notes of the major scale and the Aeolian mode is the notes of the natural minor scale.

another way to look at a mode is in terms of each one's formula, given by the letters W and H signifying whole and half-steps. Ionian's formula is WWHWWWH, so Dorian, which starts on the 2nd degree of a major scale, must have the formula WHWWWHW.

the third is to think of a mode with regard to its harmonic qualities. harmonic qualities are signified by numbers, 1 being the first degree, 2 the second up to 7. 8 is an octave above the root so it is the same note as the root, or tonic. thus there are seven modes total. a major scale's degrees are 12345678. if you look back at the formulas, you will notice that this indicates a half-step between the 3rd and 4th degrees and another between the 7th and 8th. thus the arpeggio of this scale (1357) yields a major 7th chord.

the ionian is the only mode without an accidental (a sharp (#) or flat (b))therefore the "rest" of the modes are created by raising or lowering one more degrees in the ionian mode. in addition to Ionian, two of the remaining modes are major scales (meaning they have a major third, which is two whole steps above its tonic), Lydian and Mixolydian, starting on the 4th and 5th degrees of the Ionian mode. the Lydian is a major scale with a raised fourth degree (123#45678). Mixolydian is a major scale with a lowered seventh degree (123456b78). its arpeggio yields a dominant seventh chord (135b7), an EXTREMELY common chord, used in practically every blues, funk, and jazz song.

the remaining 4 modes are minor scales. Aeolian is a natural minor scale (12b345b6b7). dorian is a natural minor scale with a raised 6th degree; phrygian is one with flat 2nd; and locrian one with a flat 2nd and 5th degree (meaning its formula is 1b2b34b5b6b78!!).

Each mode thus corresponds to each of the chords its arpeggio implies. Ionian fits over a major sevent chord (1357), dorian a minor 7th chord (1b35b7) etc. etc. etc.!!!!!!!!!!!!!!!!!!!!!

in conclusion, perhaps the only difference between a scale and a mode is that a scale is just the actual instance of any mode in context, e.g. the Ab major scale, or Bb Dorian scale.

Ionion - Just add 4th and 7th to major pentatonic.
Dorian - Just add 2nd and 6th to minor pentatonic
Phrygian - Just add b2nd and b6th to minor pentatonic
Lydian - Just add #4 and 7th to major pentatonic
Mixolydian - Just add 4th and b7th to major pentatonic
Aeolian - Just add 2nd and b6th to minor pentatonic

The locrian is slightly different, the way I think of it is that the locrian is based on the 7th degree of the major scale.

E.g C Locrian is from the Db major scale (C is the 7th degree of the Db major scale) and I just add the 4th and 7th to the Db major pentatonic.

I think the key to understanding modes is to make up your own little way of thinking about how they work, there are lots of ways of approaching modes. As a classical guitarist I always think of them in relation to other scales that I know; playing classical guitar I think of them in relation to major/minor scales. In a rock context I usually look at them in relation to pentatonics as described above. Which I guess is a little stange.

Blah, music theory is such a horrible thing to explain, don't fancy ending up as a music teacher!

in parlance, one plays a scale, but one does not play a mode, any more than one plays the key. the key is established by the ear guessing which of the chords played or implied is the root; the mode of the melody is then figured out...

one might say of coltrane, 'he just plays scales'; one might remark of miles, 'here he replays the melody in the phrygian mode'

remember the basic meanings of the words:
scale = the 'ladder' of notes... definitely a noun, a concrete instance
mode = the 'fashion' or 'mood' of the scale or melody being played... more like an adjective...

take a melody and move it from one mode to another. you can still recognize it, sure, but it sounds a bit off.

if instead you moved it from one key to another, unless you have perfect pitch, [or its playing over the rest of the song which remains in the old key], you won't really be able to tell the difference, except you'll say, "that sounds higher" [or lower].

Mig, you're right to say it gets confusing without examples. I guess the main reason I asked is because I've always wanted to understand what it means when so-or-so plays 'modal' jazz....

I'm a little closer to understanding; but the natural follow-up would be:

What's a good example of modal music? As contrasted to what? What about modal folk? Or Rock? Or Pop? etc

A mode is always a scale (ie can be played in the form of a scale).

But a scale is not always a mode (the chromatic scale, the diminished scale, etc are not modes).

You have to be wary of generalising about "modes" and "modal jazz" as if they were describing the same thing:

- jazz played on a protracted Dorian harmony ("So What" or "Impressions") would be called modal. It would also be modal in terms of Classical music theory since Dorian is one of the Medieval modes.

- jazz played on a protracted melodic minor harmony would is also liable to be described as "modal" jazz. But the melodic minor scale isn't a "mode" in the Classical sense.

The characteristics of modal jazz are few chords, static harmony, no functional harmony or home key. The implied scale need not be a "mode".