Credit for songs

This is probably a really noob question, but I've been thinking a bit about it:

After a song title, it’ll have credit to whoever wrote the song. My question is, what exactly does writing the song mean? Does it mean they came up with the chords for the song? Does it mean they came out with the layout? Does it mean they literally played the whole song? Or they just pretty much made up the riffs and chords and stuff?

It widely depends on the open-ness of the act doing the song. The Beatles, for instance, had their 'Lennon-McCartney' thing going on, but more often than not one of them wrote almost all of the song and the other added a couple of lines here and there.

On DSOTM, the credits next to the songs are the musical credits, since there is another seperate credit that says 'All lyrics by Roger Waters'.

Radiohead claims that the band writes the songs, and also says that Thom Yorke writes the lyrics.

There's a lot of examples, but it can (almost) be guaranteed that whoever has the credit at least started the song and/or wrote the lyrics. And in a lot of music, simply performing on the track doesn't get that person a credit.

Usually, it's so.

The writer of a song is the one who writes both the music (the tune) and the words. Of course, a song can have more co-writers. For example, when you read "Comfortably Numb (Gilmour-Waters)" it means that Gilmour and Waters wrote the music and the words of Comfortably Numb.

The arranger makes the song from what above. For example, chords so, bass here, keyboards there, guitar-solo here, etc. When you hear the same song in two different ways (for example, Comfortably Numb from Live in Berlin and from Pulse) it's because of two different arrangements.

The musicians play what the arranger has made up.

At last, the vocalist sings upon the music recorded.

Only the song-writers own the royalties, but the earnings from a song can be shared with other people (producer, record-company, etc) according to different agreements.

Sorry, Shane, you posted right whilst I was typing.

That's okay, I think you explained it better than I.

Did I?

Sure. You actually gave the process while I ponied around and gave examples.

Except Dave Gilmour didn't write the Comfortably Numb lyrics... The Wall also has that cute "All lyrics by Roger Waters" legend.

yes, when you see the "all written by roger waters", it leads you to believe that he was some kind of lyrical genious... oh wait a minute...