Halliday & Matthiessen (2014: 89n):
Some grammarians have used the terms Topic and Comment instead of Theme and Rheme. But the Topic–Comment terminology carries rather different connotations. The label ‘Topic’ usually refers to only one particular kind of Theme, the ‘topical Theme’; and it tends to be used as a cover term for two concepts that are functionally distinct, one being that of Theme and the other being that of Given. It seems preferable to retain the earlier terminology of Theme–Rheme. In the generative linguistic literature, Gruber (1976: 38) introduced the term ‘theme’ in an experiential (rather than textual) sense for a kind of participant role, a ‘theta role’ in generative terms. In work drawing on Fillmore’s (1968) ‘case grammar’, the term ‘theme’ has also been used as a label for deep case, or semantic case. In a different context, ‘theme’ is also used as the name of a stratum in verbal art: see Hasan (1985b: 96).