The term rank scale was developed by

Michael Halliday Michael Alexander Kirkwood Halliday (often M. A. K. Halliday; 13 April 1925 – 15 April 2018) was a British linguist who developed the internationally influential systemic functional linguistics (SFL) model of language. His grammatical descri ...

and is associated with

systemic functional linguistics Systemic functional linguistics (SFL) is an approach to linguistics, among functional linguistics, that considers language as a social semiotic system. It was devised by Michael Halliday, who took the notion of system from J. R. Firth, his ...

, the school of linguistic theory and description of which he is the originator. According to this theory, ''systems'' are a key organising feature of grammar, and each system originates "at a particular rank: clause, phrase, group and their associated complexes".Halliday, M.A.K., and C.M.I.M. Matthiessen (2004).
An introduction to functional grammar
', 3d ed., London, Arnold, pp. 31 and 588.

References

Systemic functional linguistics {{sociolinguistics-stub