It’s like asking why singers use more than two notes to sing a song. Because it’s more interesting, it’s more fun, it’s enjoyable, it sounds better than staying in the same key for an entire song.
And most of all, because they heard somebody else do it, and they liked it.
http://lyrics.wikia.com/Da_Vinci’s_Notebook:Title_Of_The_Song
https://www.youtube.com/watch?v=281ax7Ovlsg
“Modulation, and I hold a high note!”
I’m with everyone else who is curious that people don’t find this completely obvious when the key changes in the middle of a song.
NOFX use this to a fun extent in the song Thank God it’s Monday where they announce it with the lyric “modulation/Give me another key” at 1:02
Doesn’t Barry Manilow do this in every dadgum song?
That’s why “So What,” mentioned earlier, doesn’t fit in this discussion. the I-IIb-I change is the form of the verse; the key does not change from verse to verse.
The “Gilligan’s Island” theme song is a funny one: every verse goes up a semitone.
True, but it shares the similarity with true modulation in that the same melody is played (by both trumpet and bass), just transposed, in both chord contexts.
This is rather akin to a baroque fugue, where a melodic phrase is played, and then played again starting at a different pitch (the difference is, they overlap, creating freaky and/or beautiful intervals).
It’s an uphill climb! 
If you don’t have at least some kind of musical ability or background, you may not.
I posed my Beatles modulation trivia question to a girl I know who is a passionate Beatles fan, and knows their songs (most especially their lyrics) inside and out.
Not only did she not grasp the question; when I gave her the answers, she still couldn’t “hear” what it was I was talking about, even when I told her exactly where to listen.
Here’s a great, impressive video called (what else?) “Epic Key Changes”. It’s a group covering a few songs that have those in them.
PS: MOST of the videos that channel does are amazing and awesome.
Well, not usually. In C, the blues scale is C, Eb, F, F#/Gb, G, Bb. It’s pretty typical to just stick to that scale and play it over I, IV, and V. Now, of course you can throw in all sorts of notes–and I personally do, depending on the feel I’m going for (as a piano player). Sticking to the C blues scale gives me a more “swampy” feel. Throwing in the major third, the major sixth, and changing around my blues scale choices for the chords puts me more in the mind of upbeat New Orleans style blues. But typically, as I was taught and my blues guitarist friends were taught, you stuck to the blues scale of the key over the I, IV, and V chords.
At any rate, you’re not changing the key in a I-IV-V progression. The tonic stays put.
Here is a rockin’ song that does it too.
mmm
If I was familiar with his work, I might know, but besides “Copacabana,” I don’t know that I know any of his songs.
It’s been my experience that the singer’s range is considered when selecting a key. I’ve only played with local musicians. But in those situations we tried to play in a key that was comfortable for the singer.
Professionals have wider ranges but even then the singer’s preference is important. If Linda Ronstadt wants to sing in C whos going to tell her no, “sing it in G”. She does have a wide range and could sing in other keys if the band didn’t have time to rehearse in a different key.
This reminds me that Judas Priest used this technique frequently, bumping the key up a full step for the guitar solo and then dropping back to the original key when the vocals resume. It had the effect of injecting a sense of urgency into the solo, as well as creating a tension that was subsequently relieved with the return to the original key.
It’s fairly well-known amongst musicians that different keys have different “feels” to them. Like, D-minor is the “saddest” key (Spinal Tap, “Lick My Love Pump”), and B-minor is very “tense” (which is why I think so many Judas Priest songs modulate from A-major into B-minor for the guitar solo, as mentioned above). I used a similar technique on one of my “original” songs. Several years back I embarked on a project to compose new music for old Christian hymns. I randomly flipped through an old hymnal, and made a point of selecting hymns with lyrics that engaged me, but that I had never heard (so that I wouldn’t be influenced by the original tunes). One problem with hymns is that the music is exactly the same from one verse to the next, regardless of each verse’s subject matter, and in my opinion, the music doesn’t always match up with the words. So I found a hymn called, “Hallelujah, What a Saviour”, and carefully read the lyrics so that I could compose new music that reflected those words. One thing that caught my attention about that hymn was that the first three verses were “sorrowful”, but the fourth and final verse was “triumphant”.
So what I did was compose the music in E-minor. The music behind the first verse is very simple and sparse, and then becomes more complex and “intense” with each subsequent verse. It all leads into a dramatic shift at the end of the third verse, transitioning into E-Major, and I think it really reflects the “triumphant” feel of the final verse’s lyrics.
I did finally play the original tune, and was depressed to discover that it felt more like a “marching band” song.
I play bass guitar at my church, and we frequently modulate the key up for the final verse or two of the hymn.
I find this thread interesting because I’m not sure I’m entirely clear on what’s meant. Are we talking about a singer doing something like this (most notably at 01:52 but also 00:32 and 01:11) that irritates the hell out of me for ruining an otherwise good song? If not, what would you call this vocal sin?
I’m actually not entirely clear what you’re picking up on there. Can you describe it a bit more? The vocals sound fine to me. Maybe a bit wobbly on the pitch on that first example, but nothing that really bugs me (for this type of music).
Yup, there’s a thread around here somewhere in which people are discussing the idea of picking out a melody on a keyboard, and it was in that thread that I discovered that it doesn’t require literal tone-deafness to be completely unable to pull this off, indeed, unable to tell when what they’re playing doesn’t actually sound like the melody they’re trying to pick out. This includes accomplished musicians in some cases! Some people, while they do hear music as music, just don’t, (I’m actually not sure what it is they’re not doing–matching pitches? holding a pitch in their mind while listening to other pitches? I’m not sure).
There’s a brief modulation I’m always happy to run into, for some probably odd reason. It’s the one where you’re playing a song in the key of G and in one line you switch to a E major to A major and then you’re back at the D, which is the V chord in the key of G.
Or Alice’s Restaurant does this in C. C - A - D7 - G - C. Okay, I’ve omitted some 6ths and stuff, but there it is.
Well, as I said. When you get to the blues, “key” is a pretty loose idea, and I made the mistake of not being specific.
The scale moves with the chord change a lot of the time (e.g. Long Grey Mare). Dazed and Confused does this, as well. Either those songs are chromatic, or the guitar/bass patterns are following the key of the root note.
But I get that it’s not the same thing or serving the same function as key modulation does in diatonic music. Going back to the I is still satisfying.
I’ve long felt that roman numeral analysis was a poor tool for describing a lot of blues songs. I-IV-V does a good job of describing where you’re going, not what you’re going to do when you get there. I’m not sure why I thought it was a good idea to put it in here. I blame the beer, the whiskey was just a bystander.
We might be talking about different things. Of course the chords change, and the accompaniament notes to that follow the chord. But if you listen to that harmonica solo, that’s all using the same blues scale based on the I. There’s different target notes, of course, depending on where you are in the progression, but part of that real down-home blues sound (in my opinion) comes from sticking to the I blues scale and clashing it/creating tension against the moving chord progression underneath. Shifting from I to IV to V blues scales per chord in the melody works, too, but has a different sound. Like I said, I personally use a combination of methods depending on the sound I’m going for. If it’s really traditional sounding blues, then I stick with the I blues scale for the most part.
But, anyhow, you’re right. Western harmonic theory leaves a bit to be desired when talking blues, but there still is a sense of key, even if major/minor tonality can be a bit ambiguous.