Themes consist of simple theme, multiple theme, and clause theme, and have three metafuntions: textual metafunction, interpersonal metafunction, and experiential metafunction.

• 功能语法学派普遍认为，主位可分为简单主位、多重主位和句式主位，同时主位具有语篇纯理功能、人际纯理功能和经验纯理功能三大纯理功能。