Lydian vs. Locrian

Back in the day when the church controlled the world, people weren't allowed to write music based on the locrian mode, on account of its flatted fifth (The Devil's Interval), yet the Lydian was perfectly acceptable despite its sharped fourth, which is the same note! Does anyone care to explain?

Although, there may be a longer more historical correct answer to this. I think it just goes more by what scales are used more in a particular style of music. Certain scales fit good with certain music, and some don't. You may see this if you learn more exotic scales, you may find that they may not work well with the type of music you wanna play. Unless you wanna be different, but in thoses days it wasn't easy to be different. The church was ten times more strict then, so anything they didn't agree with was forbidden.

Another thing, the locrian is different because of there root and the pattern that follows. This will give the scale a certain sound (tonality). Same with the lydian, it's the sound of the scale. They just probably thought it didn't sound good for church music. The sharped 4th and the flattened 5th are the same sound, but it's the relationship with the scale that gives it a different tonality. Like Relative minor and major, although they have the same notes, they're tonality is different.

I thought the notes of the Eb tritone were supposed to be the devil's notes? All well. Its silly anyway. No flatted 5th, that means no diminished chords either. Weird.
Music history would be cool to study.

i was reading some site that said it was the 4th note? why would you have a flattened 4th note?
"fourth was considered being the interval of THE DEVIL"
at this site : http://home.swipnet.se/freakguitar/lydian.html

Flattened fourth notes are extremely rarely, and is only found in the diminshed whole tone scale (super locrain). Not even the chromatic scale has the spelling flat fourth. It's almost always spelled as a major 3rd. Plus, I was always told it was the flattened fifth that was the devils interval. Just play it, it sort of has a evilish sound to it. And I bet back in those days, if you sat and played it over and over on a church organ. You would probably freak everyone out. :D

There were diminished arpegios in classical music... Beethoven's "Fifth Symphony" & Bach's "Toccata & Fugue In Dm" had some diminished lines.

Roughly, around the 1980's a book became quite popular.
"The Lydian Chromatic Concept", by George Russell. I am not at all certain I ascribe to these ideas, but it's still quite interesting. He was an awesome player in jazz. My understanding, he was a hard man to get to know. And a hard man to please, playing wise. That I can attest.

This may be an over simplification, but in terms of modern music or the music of the last 50 years the tritone is a dominant substitution. e.g., G7 and Db7 are, in the simplest term the same chord. The actual tritone are the same notes. That's how they relate. The 3rd and 7th of each chord are the same. All the other notes are incidental. A simple guitar blues bass line is made from this idea.
B7, E7,Bb7,Eb7,A7,D7,Ab7,Db7,G7,C7, and so forth. Play bass root plus tritone. On guitar you can visualize and hear the idea.

History of music, modes....

That's almost a post for Azrael :)