Well, what I mean is we've only gone over major scales in class, so those are the only ones I'm familiar with. I've also seen the scales in the "Fretboard Logic" book, which I think are called pentatonic scales (maybe), so I know those, too.
You guys are all talking about progressions and IV chords and stuff like that and I really don't know what that means. In piano, we've been going over triads and inverting them. As far as guitar is concerned, I know the standard major chords and the main minor variations of a couple of them and also power chords, but beyond that I'm pretty clueless as to how all this stuff works. I downloaded this program for my ipod that's supposed to help me learn (by ear) intervals and chords and scales (whether it's a major/minor etc, not if it's a D or whatever). So I guess what I'm saying is I only have a very basic understanding of notes. When we (my band) write songs, we basically just come up with a cool sounding riff and then build on that with other things that sound good together.
For an example, in one of our songs, I can basically play an open D power chord (dropped tuning) for the whole song, but when I'm playing real chords for a different part, it goes Dm->Am->Dm (except without the F this time). Would that be in D or in Dm? This is all very confusing to me...
That song would
probably be in D minor, because a D power chord (D5) isn't major or minor. There's only a root and 5th in the chord; the 3rd is what determines major or minor.
However, it could be in both. It would depend what the vocal melody is over the D5 part. He could be singing a melody with F# in in, which would give it a major sound, or it could be an F natural, which would give it a minor sound. Modal mixture (mixing chords/notes from major and minor) is fairly common in alternative music like Nirvana and a lot of 60s pop rock like Beatles and stuff.
It's not always possible to tell what key a song is by seeing the chords. Sometimes you have to hear the melody too. Even sometimes sheet music will have a key signature of 2 sharps, which would indicate D major (or B minor), but the song is actually in the key of A. It just so happens that it has a Mixolydian sound and uses
G natural notes so often that they wrote the song in that key to save from having to write a bunch of accidentals.
For instance, you might see a song with the chords A, G, and D. A strict diatonic approach would say that's a V, IV, and I chord in D major. But if you hear the song, it might be clear that A is actually the tonic because of how the vocal melody cadences, etc. So the chord progression would actually be analyzed as I, bVII, IV.
I know this may be a little over your head at this point, but all I'm saying is that it's not
always as easy as looking at sheet music or seeing a chord chart. I work in the music publishing business, and believe me, there can be mistakes in sheet music---including misleading key signatures.
Having said all that, do a search on the net for "determining key center" or "figuring out the key of a song" and you'll probably come across some chord theory that tells you the diatonic chord formula: I is major, ii is minor, iii is minor, IV is major, V is major, vi is minor, viiº is dimished, etc. Then, by looking at the chords of a song, it's usually easy to determine the key, because they will only fit within one or two keys. However, as I said, this approach is not failsafe. This system would tell you that the chords I listed above are in D major, which is not always the case.