Does that mean that C minor has Eb major and Eb minor? And no D#?

A good point on the notation; avoiding duplicate letters is more than just a convention.

The main reason for all this...each note used diatonically will have its own line or space Source? IMO it's more fundamental than that: That's what "scale" means: it goes up and down - doesn't stay on the same degree twice. I don't really agree that convenience for notation should determine the definition of a scale.

@Stinkfoot - why would a source need to be provided? It's what happens! Scale means ladder - notes moving up and down sequentially. There's probably no mention that each rung has to have a different letter! What would your definition of a scale be - and that's not exactly what was alluded to in this answer. It certainly makes as much- if not more practical - sense that way.

@SovereignSun - your comment question makes no sense to me.

@Tim - you offered our notational conventions as an explanation for the structure of scales. On that I am asking for a source. "It works well" is not a source, and I explained why I'm doubtful about your explanation.

@Stinkfoot - the structure of scales is the sound of each note. What actually sounds right. That's a good start point. Then, they need annotating. What better, logical, easily understood, simple to write and read, way is there?

@Tim - I think you are missing my point. Enough.

@SovereignSun - one note by itself - Eb - is neither major nor minor. The 3rd degree of the C Minor scale is Eb. The note is Eb - period. Its interval from the root - C - is a m3rd, as opposed to E, found in the C major scale - its interval is a M3rd. There is no D# in C Minor or C Major: D is a 2nd counting from C. Both CM and Cm contain the interval of a Major 2nd - D. D# would be an augmented 2nd. Neither CM nor Cm contains an augmented 2nd.

@SovereignSun (cont) : A major scale is not comprised only of major intervals, nor is a minor scale comprised only of minor intervals. Major scales contain minor intervals: from a M3rd to a P4th is a minor 2nd; From m6 to m7 is a Major 2nd. A scale is called "Major" or "Minor" based on its overall structure/sonority (particularly its 3rds and 7ths), not because all its intervals are major or minor.

@SovereignSun - continuing Stinkfoot's comment, there is also an augmented 2nd in the harmonic minor scale - from its 6th to raised 7th note. Again, it won't be thought of as a minor third !

As long as I understand a scale should have all 7 notes. So if it's a scale with sharps then still the notes will be flat, except white keys? I still don't get it. If I am playing Bm, then after do I play a F#m or a Gbm? When I see chords to songs it is always Bm - F#m.

@SovereignSun - oh, Sovereign Sun, it's quite simple. Let's take the key of D major, with two sharps, F# and C#. As a keyboard player, simply, slowly, play the scale notes from D. The third note you hit will be F#. Not F. What you've done is go past that F to a higher note, which will be called F something, as it's the F that's changed. Yes, F#. The same thing happens with the C. It needs to be higher, so is C#.

@SovereignSun - now let's take Bb major. Start on that note - and call it Bb not A# !! Next comes a C (ordinary, natural) then a D, then some sort of E. The one that sounds right - 'cos it is - will be Eb. Can't be D# in this situation, as you already played a D note. After that, it's plain sailing with natural notes till you need another B of sorts. Got to be Bb - you already used an A !! Each and every (major) key has its own # or b, and they do not get muddled. Learn each key sig., and you're nearly all there!

@SovereignSun - those black keys are both # and/or b at the same time, but they only, usually, get called one or the other in one key. If you played the violin, then you may find that, say, Bb and A# are indeed slightly different notes. But that can't happen on keyboard - it's a bit of a compromise. Check out equal temperament. Please!

@SovereignSun - of course it will be a mistake - and wrong! We call the chords and notes by the names they are given in a particular key. In B maj there's A#, but in Bb maj key, it ought to be called Bb. It's bad to call things wrong. To your son, you are father, but to your dad, you are son. Same person, different situation. Have to say that a lot of guitarists seem to live in a 'sharp' world, where flats are what you may live in, so maybe that's where it all started to go strange.

@SovereignSun Is it bad to name notes incorrectly? God is not going to punish you for naming notes incorrectly. :) But you will not be well understood, just as if you used incorrect words to express yourself. Your thinking about music will also be skewed - you will never grasp the fundamentals of our theoretical system of music unless you learn how name notes, scales and chords correctly, and refer to them that way.

@SovereignSun (cont) These things are really not very difficult - if you are a programmer, it is easier than most programming languages. But I strongly suggest you find a good book or a teacher so you can learn properly. People often show up on this site very confused because they have not taken a serious, organized approach to studying music and grab snippets from different not necessarily reliable websites. That is not how to do it. There are many books. I like "Music Theory for Dummies" - it follows the pattern of a college music curriculum and is well written and organized.

@Stinkfoot Okay. I will have a look at it. Thank you.