Coordination and subordination are the two fundamental mechanisms for combining clauses in English. They produce different structural relationships and carry different discourse implications.
Coordination joins grammatically equal elements using coordinating conjunctions: and, but, or, nor, yet, so, for (the FANBOYS).
Coordinated clauses are independent; each could stand alone as a sentence. Coordination is characteristic of spoken English and simpler written registers.
Subordination embeds one clause (the dependent/subordinate clause) within another (the main/independent clause). The subordinate clause cannot stand alone.
| Type | Conjunctions | Example |
|---|---|---|
| Adverbial | because, although, when, while, if, unless, so that, in order to | Although it rained, we went out. |
| Relative | who, which, that, whose, where, when | The book that I read was excellent. |
| Noun | that, whether, if, wh-words | I know that she left. |
Subordination creates hierarchical structure: the subordinate clause modifies or completes the main clause. See Embedding for the recursive nature of this process.
The subordination index (ratio of subordinate clauses to total clauses or T-units) has been used as a measure of syntactic complexity in L2 writing research (Hunt 1965). Higher subordination ratios correlate with writing development up to intermediate levels. However, recent research (Kyle & Crossley 2018) suggests that at advanced levels, phrasal complexity within the Noun Phrase becomes a stronger indicator of writing quality than clausal subordination.
Paired conjunctions coordinate elements with added emphasis:
These require parallel structure, a frequent source of L2 errors: Not only did she study hard, but she also passed (note the Inversion after not only).