@article{Halliday70-functionaldiversity,
  author	= {Halliday, Michael A. K.},
  year		= {1970},
  title		= {Functional diversity in language, as seen from a consideration of modality and mood in English},
  journal	= {Foundations of Language},
  volume	= {6},
  number	= {3},
  pages		= {322--361}
}