Intervals Journey - Chapter Iii "another Question" Options

[MonkeyDAthos]

Hi, Gmc.
Lately have been without internet, so i decide to dedicate a bit to resume my intervals studies. but once again, i am confuse as hell.
here's the situation.

(PS: correct me if i am wrong)


Intervals:

Root
2º minor = 0,5 (one half'step from the Root)
2º major = 1 (two half'steps or one whole step from the Root)
3º minor = 1,5
3º major = 2
4º perfect = 2,5
4º Aug/5º Dim aka Tritone = 3
5º perfect = 3,5
5º Aug/6º minor = 4
6º major/7º Dim = 4,5
7º minor = 5
7º major = 5,5
Octave = 6


So far so good.
The Problem comes now.


I read, that if you expand a perfect interval by a half step, it became's a Aug Interval

and if you contract it by a half step it became' Dim.

Now for example you have a C(root) and F ( perfect fourth interval) now add a Flat on the F it become's Fb.

and the invertal change from this to this

E E
B B
G G
D 3 = D 2
A 3 A 3
E E~


Before "studying this, i would say that if you contract and perfect fourth by a half step, the interval would transform into a 3º Major nor a Dim 4. Because of the table of interval i wrote up there.
(3º major = 2
4º perfect = 2,5)

So? Hows gonna be? can you assume that 3º Major and a Dim 4º are enharmonic equivalents?
Becoming something like
3º major/ 4º Dim = 2
4º perfect = 2,5

or is there something else that, i am missing?

Same stuff confuse me, on Expansion and Contraction of Major/Minor Intervals.

For example you have a 2º Major and expand it by a half step it would or should became a Aug Second.

so i got 3 freaking name to the same interval >: o Aug Second/Major Third/ Dim Fourth.


So are they all enharmonic equivalents, changing the name. depending of the situation? or is there anything else i should know?

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This post has been edited by MonkeyDAthos: Aug 9 2011, 08:56 PM