>e.t.c.

This is an abbreviation, and its two-fold meaning should be obvious.

First, following as it does my hasty list of certain keys in music I do not understand, it means "experts to clarify".

Second, it means, "excluding the carrots", since, as I am sure you will agree, carrots have absolutely nothing to do with the subject at hand.

Duh.

: )

Sharps and flats go with the letters (A - G); any of them can be major or minor.

How can you tell what key a piece of sheet music is written in?

Do these three things:

1. Look at the key signature
2. look at the final chord
3. look at the music

The key signature will indicate the scale that is used. However, there are two possible keys for every key signature. For example, the key signature of one sharp (an f#) may be that of G Major or that of e minor. What you have to find out is where the center of tonality is. If you look at the music and see accidentals written in that are leading tones in the minor key, such as d# in the key of e minor, that may indicate the minor key as a tonal center. Look at the final chord. Most often it will be that of the tonal center. So in this example if the piece ended on an e minor chord, it would most likely be in the key of e minor.

There are always variations and pieces that end on chords other than the tonal center. Most of the time, the above method will work. To be more accurate in finding the key, you need to understand more about cadences, scale tone triads, and harmonic progressions. In any case you need to know your scales and key signatures.

From:
Music Theory Questions and Answers

However, there are two possible keys for every key signature. For example, the key signature of one sharp (an f#) may be that of G Major or that of e minor. {emphasis mine}

I like to think of (and subsequently hear) key centers as functions of mode. It leaves a lot more sounds available to the ear than the simple "western" major-minor perspective. Dorian, keeping with the same example, which starts on an "A" but also uses only the "f#" alteration, gives a much more uplifting, focusing... almost centering effect without need for further harmonic resolution "along the way", and it acheives this with 6 out of the same 7 tone relationships. (Not withstanding "western" intervention to alter it as per the habits of the aeolian/ionian history... in essence, robbing it of it's natural beauty or at least prostituting it to enhance thier own shortcomings) .

I say, without hesitation, that the raised sixth of the dorain scale is a *force to be reckoned with, the doorway to a different aural experience I'm reminded of as I sing it to myself...

There are seven modes of the sort that musick was talking about with his comments on Dorian. One way of looking at them is to think of the white keys on a piano. The mode with the scale starting (AKA the tonic) on D is called the Dorian. The rest are:
Code:

---

Tonic   Name
  E    Phrygian
  F    Lydian
  G    Mixolydian
  A    Aeolian
  B    Locrian
  C    Ionian

---

Another way of looking at them is to analyze them as major or minor keys with one (or more) notes off.

Dorian is minor with a raised 6th.
Phrygian is minor with a lowered second.
Lydian is major with a raised fourth.
Mixolydian is major with a lowered seventh.
Aeolian is the pure minor without the jiggery-pokery done to the standard harmonic or melodic minors of regular music.
Locrian is minor with a lowered second and a lowered fifth*
Ionian is the good old standard major scale.

*This lowered (or diminished, to use the technical term) fifth is what scares most people away. It was considered evil and not used in the church modes of chant. The interval of a diminished fifth, however, is not all that uncommon in later (Renaissance and newer) music, often being used to suggest some foreboding. For example, in the Schubert A-flat Mass the basses get to sing a diminished fifth in the Credo on the word Pontio when singing of the belief in the crucifixion of Jesus.

Musick, Faldage -- Are you music professors?