I see a lot of bogus advice on the internet about learning scales and (shudder) modes. Some of it's just plain wrong: amateurs who've got a confused idea about something and seen fit to post a "lesson" to communicate their misunderstandings to others. But some of it isn't exactly wrong but it's still massively unhelpful, because it removes theory from practice.

What Music Theory Is

Consider the claim that a mode is a scale played starting and ending on some particular note; for example, D Dorian is C major played from D to D. Now, on its face this is just false -- you can play melodies in D Dorian starting and ending on any notes you like. We all know this. So we can safely write off anyone who says it as an idiot.

Or can we? If we try, they will wriggle out of it. It's not a statement about how to play a Dorian scale, they will say. It's a theoretical definition of what Dorian is. But the truth is, this isn't a valid way define things at all.

In linguistics we make a distinction between prescriptive and descriptive approaches. The former aim to tell us how we should use language. You start with an abstract theory and force the practice to fit it. It's mostly the preserve of retired colonels who write to newspapers decrying how the country's going to the dogs because young people don't know how to use "whom" correctly.

Music theory is a descriptive discipline. Exclusively. No reputable music theorist will tell you what music ought to be. What they will tell you is some aspects of how, in fact, a certain group of people made music at a particular time (including the present). The abstract concepts of music theory come directly from observations of actual practice.

The advice about modes starting and ending on specific notes just can't have come from the descriptive side of things because it's not what people actually do. I defy you to find any example of a player who runs modes from root note to root note on a regular basis. It sounds terrible. Nobody competent does it.

So when someone tells you that a bad definition is actually good because it's only theoretical, don't take it on board. Theory arises from practice, not vice versa. If it doesn't work in practice, it has no place at all in theory.

(Aside: In fact the starting-and-ending-on-a-given-note thing comes from a misunderstanding about how scales are printed in textbooks. This is a great example of mistaking music theory for a branch of pure mathematics. It's a solid-gold, 100% reliable acid test for people who don't know what they're talking about. But that's not my main topic here.)

Do You Know That Scale?

Here's the simple test of whether someone has given you good advice about scales and modes and whatnot: will it enable you to learn the scale? I mean really learn it.

This means that given a fret number and a root note, you should be able to instantly play the required scale there. And every note you play, you should know what it is relative to the root note (i.e. what chord tone it is). I do mean instantly. Half a second delay is too slow; on a 240bpm bebop tune that's half a bar.

If a "theory" explanation actually prevents you from doing this, it is not worth wasting your time on. This includes any and all "theories" that require you to calculate things before you play them: there's no time to do that in real music-making.

Many beginners are confused by what they read on the internet for very good reasons. They see (one way or another) that what's been presented to them can't really be applied to practical music-making. The only thing they've done wrong here is blaming themselves. Their confusion is well-motivated, and they should stop reading whatever they're reading and find a better source of information.