Two Voices on One Staff Renders with Two Staffs

Question

In my piece I want to have two voices on one staff, with lyrics, like in the docs.

But lilypond tries to create two staves like on a ChoirStaff.

\version "2.19.80"
\language "english"

signature = {
    \key c \minor
}

soprano = {
    \signature
    \voiceOne
    g f e f
}

alto = {
    \voiceTwo
  e b e c
}

verseOne = \lyricmode {
This is a song
}

verseTwo = \lyricmode {
A- no- ther verse
}
verseThree = \lyricmode {
One last verse here
}

\score {
<<
\new Staff 
  \new voice = "soprano" \soprano \relative c'
  \new voice = "alto" \alto \relative c'

  \new Lyrics \lyricsto "soprano" \verseOne
  \new Lyrics \lyricsto "soprano" \verseTwo
  \new Lyrics \lyricsto "soprano" \verseThree
>>
}

There are three verses to the song, and I want to have the soprano stems go up and the alto stems go down.

What do I do?

Answer 1

You need to add grouping to your staff using << ... >>. (The basic idea is that adding << ... >> when structuring the score is rarely harmful.

Also, note that \relative c' should be before the notes to be "relativised" and not after; this is general to any LilyPond functions.

Working code:

\version "2.19.80"
\language "english"

signature = {
    \key c \minor
}

soprano = {
    \signature
    \voiceOne
    g f e f
}

alto = {
    \signature
    \voiceTwo
    e b e c
}


\score { <<
    \new Staff <<
        \new Voice = "soprano"
            \relative e' \soprano
        \new Voice = "alto"
            \relative g' \alto
    >>
    \new Lyrics \lyricsto "soprano" { a b c d }
    \new Lyrics \lyricsto "soprano" { aa bb cc dd }
    \new Lyrics \lyricsto "soprano" { aaa bbb ccc ddd }
>> }