Modes and Scales
 

I've been learning about music theory, and there's one thing that is bugging me. A major scale in C for exemple has the following notes CDEFGAB, however a dorian D scale also has the same notes DEFGABC and aswell does the relative minor A, ABCDEFG (none having sharps or flats of course)... For each major scale there are 6 other modes that have the same notes. So my question is, what makes it so that we call a scale "Dorian" for exemple when it could just be called a major scale in another key.

Well, that's the thing. A scale is always a consistent set of intervals -- Ionian is when you start from the first and go all the way to the eighth (or one again). When you go from second to second (or ninth), it's Dorian.

So D Dorian is technically C major (or Ionian). But couldn't you also say that C Ionian is technically just D Dorian?

3rd to 3rd = Phrygian, 4th to 4th = Lydian, 5th to 5th = Mixolydian, 6th to 6th = Aeolian (minor), 7th to 7th = Locrian

They're all intertwined due to the fact that D Dorian basically means 'Take D major and flatten the 3rd and 7th'. And when you do that with D, it's basically like playing D to D with no sharps/flats (or in C major). Music theory is a concept that's dodgy, but once it's grasped it's almost permanent.

I'm pretty sure I understood everything you said, but let me ask my question in another way. The song Light my Fire, is said to be written in Dorian mode. The chords in the verses according to this tab are Am and F#, and in the Chorus GAD and ends with GAE.
So if this is played in an E Dorian scale, then the verses are a IV-II progression and the chorus is a III-IV-VII / III-IV-I progression. According to wiki (not always best reference) this is written in Dorian, why couldn't it be in Ionian (Major) with a verse being V-III and a chorus being IV-V-I / IV-V-II. What rules are set in place for this to be called Dorian and not Ionian. Is it just the fact that it ends on the tonic, or are there other rules set it place?