Fb = E ?

I head a lot of musicians saying that an F flat isn't the same as an E, that a B sharp isn't the same as a C, and so on...

Why is that?

My composition teacher made a series of videos discussing this. Very controversial, I think... But, I like his theory.

Start here: https://www.youtube.com/watch?v=Yga8EEAQFqM

Technically they are not "the same" but sound the same. At least with the current (equal-tempered) tuning system.

because you can't have 2 same notes in one scale i think. so you project a certain move in your mind with this new change.

You'll want to look up the history of temperament. Until relatively recently the idea of a 12 tone equal division of the octave was foreign to music; Instead scales were built on whole number ratios which meant that not only is b sharp not c, c sharp is bot d flat. It all depends in the tonic and the individual scale degrees' relationship to it.

You'll want to look up the history of temperament. Until relatively recently the idea of a 12 tone equal division of the octave was foreign to music; Instead scales were built on whole number ratios which meant that not only is b sharp not c, c sharp is bot d flat. It all depends in the tonic and the individual scale degrees' relationship to it.

It is not possible to build a scale using only whole number ratios. When you have a fixed-pitch medium some compromises have to be made because pure intervals form a spiral (three major thirds are not an octave - twelve fifths are not seven octaves - the difference is a Pythagorean comma). Throughout history it has been a question of what is most important. In medieval times, for example, pure fifths and fourths (and consequently 9ths = whole tones) were considered to be the most essential to have, which is where Pythagorean tuning comes from, with eleven perfect fifths and fourths (and one wolf fifth/fourth). The thirds are horribly discordant which corresponds to their function in cadences in medieval music. In the Renaissance, pure thirds were valued more, enter meantone, with just thirds in the most common keys but very flat fifths and sharp fourths (and therefore whole tones as well). Because the diatonic and chromatic semitones are not the same length, special unintuitive keyboards with more than twelve notes were constructed, and these indeed contained enharmonic notes which differed in pitch, but that is not to say that C sharp is not the same as D flat in any absolute sense. Tunings and temperaments are not much more than formulas and the note names are merely abstractions. It is entirely conceivable on a twelve-note Meantone keyboard to write C sharp and D flat both in reference to the same key, but Meantone died with simple diatonic progressions and so there would be no need to notate in such a convoluted way.

In the same way, even in a non-tempered medium enharmonic notes can be identical. It has to do with function - consider writing an A major chord as A - Db - E. It is highly illogical (although Messiaen does that sort of thing all the time to my continued confusion) but in no way will the D-flat ever be rendered as anything other than C sharp unless the composer specifies otherwise. However, consider a progression that moves from A major to D flat major to a dominant seventh chord on E flat (which cadences on A flat major). In this progression, the D flat would probably not be the same pitch as the C# in the A major chord, but that is because the function of the two pitches is indicated by different signs rather than there being an intrinsic difference between sharps and flats.

It is not possible to build a scale using only whole number ratios. When you have a fixed-pitch medium some compromises have to be made because pure intervals form a spiral (three major thirds are not an octave - twelve fifths are not seven octaves - the difference is a Pythagorean comma)

Not all mediums are fixed pitch, obviously. Prior to instrumental music, as close an aproximation to just intonation as possible was definitely the norm.

And while a string section may intonate A-Db-E as a major chord if it is obviously functioning as such, it will not necessarily intonate all Db's and C#'s exactly the same. As you point out, function and context are paramount.

The point being that they are not the same thing because depending on the context they may imply different intonations. You are correct in your summarization of the history of temperament; that is the point I was trying to make originally.