Full Idea
If there is but one world, it embraces a multiplicity of contrasting aspects; if there are many worlds, the collection of them all is one. One world may be taken as many, or many worlds taken as one; whether one or many depends on the way of taking.
Gist of Idea
If the world is one it has many aspects, and if there are many worlds they will collect into one
Source
Nelson Goodman (Ways of Worldmaking [1978], 1.2)
Book Reference
Goodman,Nelson: 'Ways of Worldmaking' [Hackett 1984], p.2
A Reaction
He cites 'The Pluralistic Universe' by William James for this idea. The idea is that the distinction 'evaporates under analysis'. Parmenides seems to have thought that no features could be distinguished in the true One.