When I was writing the Encyclopoedia I was aware that a lot of guitar students find the idea of modes very confusing. I spent a bit of time working out a sensible way for guitarists (and others) to think about them, and it wasn't that hard. It therefore continues to amaze me that lots of guitarists -- even experienced teachers -- often say things about modes that are either flatly incorrect or only part of the story.
Myth 1: The Modes are the Dorian, Phrygian, Lydian...
Guitarists think this because that's what they're taught: "You've learned the Major scale, now you need to learn the modes". These things called "the modes" seem to really just be scales, don't they? So why are they called "the modes"? It's a mystery, isn't it? Just another one of those weird things about musical terminology, perhaps.
The idea of modality doesn't just apply to the Major scale modes most guitarists learn if they want to play jazz or rock. It applies to any scale: well, almost any -- there are a very small handful of exceptions. It's an extremely useful idea, and it's a real shame that most guitarists don't understand it well enough to benefit from it.
Myth 2: But "The Modes" Come From Ancient Greece!
Stop it with this. The names of the modes are derived from the names of places in ancient Greece. That's about it. If you want to hear some ancient Greek music, check out the sound files at the Australian Academy of Sciences. Beautiful, haunting and strange they surely are, but anything to do with modern Western music they surely are not.
For a start, the tunings are all different; you can actually hear MIDI having to rapidly bend the equal-tempered pitches to fit what scholars believe would be the right pitches for Greek music. That aside, the system of pitch-organisation was quite alien to modern music theory too. Modality as we understand it today wasn't even possible until the Renaissance, and was only rarely used as a concept before the twentieth century.
Myth 3: Modes are Scales
This is half true, but half-truths are dangerous.
In modern music theory the word "mode" has a precise and specific meaning. Any scale (with a very small handful of exceptions) has more than one mode. The clue's in the name: a mode has to be a mode of something. Modes don't just float around on their own.
It's more correct to the Dorian and Phrygian scales are modes of each other. So are the common Minor and Major pentatonics. So, as a matter of fact, are the m7 and major 6 arpeggios.
You can call a particular scale "the Dorian mode" if you like. I prefer "the Dorian scale", because if someone says a scale is a mode I want to ask "what of?", and that's not always a relevant question. But that's just nomenclature: you can call it anything you like as long as you know the difference between a scale and a mode.
Myth 4: A Mode is a Scale Played Starting with a Different Note
This is a very useful claim because the minute you hear it you immediately know you're dealing with someone who hasn't a clue what they're talking about. Why? Because their theory doesn't match their practice. A scale is the scale it is no matter what order you play the notes in, as the person who just confused you with this claim will prove when they pick up the guitar and show you some licks.
A Dorian scale in D is not, repeat not, a C major scale starting and ending on D. If you think it is then I'm afraid someone has lied to you and you need to wash out your brain with a bottle brush. As soon as you see this, walk away. Never listen to anyone whose theory doesn't match their practice, because that's what's called "a bad theory".
Anyone who mounts a defence by claiming that this has something to do with mediaeval chant is talking out of their hat, for similar reasons to Myth 2 (see, for instance, this useful introduction to the church modes).
Myth 5: A Mode as a Scale Played in a Different Key
Oh, sure. You can think of it that way. If you're playing over F# minor and want a Phrygian sound, you can think like this: "Well, the Phyrgian mode is the major scale played an augmented fifth above the root. The fifth of F# is C#, so the augmented fifth is D. So I can play a D major scale here".
By this time the band will have gone home.
Don't do this. It works in theory; you really will be playing F# Phrygian if you do through this contorted little thought-process. In practice, though, it fails dismally because it requires you to do way too much thinking.
So there's five myths about modes that we hear too often, and that confuse students and seasoned musicians alike. The sad thing is that the idea of modality is a fantastically useful timesaving device and a great source of new and interesting sounds. I know I've been a bit negative in this article, so I'll post an explanation of how I believe modes should be thought of in the near future.