In Systemic Functional Linguistics, the term rank can be understood as the grammatical unit of the language or text. The meaning of scale in this context is how a higher unit is made up of units from the lower rank, without skipping. The rank scale provides us with a hierarchical model of constituency where larger grammatical units are composed of smaller units.

Take a look at the featured image above, but focus on the right-hand model. The lowest rank is morpheme, while the highest rank is clause complex. Well, a clause complex is a linguistic construct consisting of more than one clause. Halliday revised his 1961 model, where he initially labeled the highest rank as sentence, to dispel the confusion between a clause and a sentence. Think of this example:

She is a wonderful woman.

Is this a sentence or a clause? The answer is both. Now, what about this example:

She is a wonderful woman, but she is also mean sometimes.

This is a sentence, but not a clause. Yet, it consists of two clauses. So, what actually distinguishes between a clause and a sentence? It is unclear. Thus, instead of using the label sentence, Halliday labels it a clause complex.

Based on the image, we can say that a word is made up of at least one morpheme. A group or phrase is made up of at least one word. A clause is made up of at least one group. But a clause complex is made up of more than one clause.

Group vs Phrase

A group is a phrase in the traditional linguistic view. In SFL, instead of saying a noun phrase, we call it a nominal group. A group is made up of at least one word. For instance, book or go. Yet, it is rarely so in real communication because a group, as with a phrase, usually has its head and a few modifiers.

SFL groups include: nominal group, verbal group, adverbial group, and adjective group. Meanwhile, the prepositional phrase remains, because this type of phrase always requires at least one group. For instance, "under the table," where "the table" is a nominal group. What about just "under"? In SFL, it is not considered a prepositional phrase, but a word (a preposition).

Rank Shift

In SFL, the rank status of a unit is not absolute. A clause, for instance, can be identified as a group. Thus, the status of a unit is not merely decided by its size, but by the rank where it functions. Consider this example:

Swimming in the pool is a form of therapy.

Regardless of the truth value, the underlined part is a clause, functioning as a subject of the larger clause. Because only nouns can be a subject and/or object, it is actually a nominal group. In SFL, this process is called rank shift: a unit from a higher rank functions within a unit from a lower rank in the rank scale.

A unit from a lower rank cannot function within a unit from a higher rank.

The highest or largest grammatical or language unit in SFL is a clause. However, it is not based on the text length, but on the meaning. Thus, in SFL, it is preferred to say that a clause is a semantic unit rather than a grammatical unit. A clause is complex when the text has more than one clause, where one expands, extends, or projects the meaning of another. For instance:

He told me that he would pay the rent today.

The underlined part projects the meaning of "told". In SFL, this part is called a Verbiage, because the "told" is a verbal process. A verbiage is simply the content of what is "said." Hopefully, we can discuss different process types in the future.

For a clearer presentation, consider watching the following video: