Clause Nexus: Primary And Secondary Clauses

Halliday & Matthiessen (2014: 441-2):

a clause complex is formed by means of tactic relations; and it is developed or built up as a chain, one pair of clauses at a time.We will refer to any one pair of clauses related by interdependency, or ‘taxis’, as a clause nexus. … The clauses making up such a nexus are primary and secondary.  The primary is the initiating clause in a paratactic nexus, and the dominant clause in a hypotactic; the secondary is the continuing clause in a paratactic nexus and the dependent clause in a hypotactic. This is set out in Table 7-4.