cohesion

Cohesion is the grammatical and lexical linking that holds a text together — the ties between sentences that make them a text rather than a pile.

Halliday and Hasan named five categories of cohesive device: reference (pronouns, demonstratives), ellipsis (omission), substitution (a general word for a specific one), lexical cohesion (repetition, synonyms), and conjunction (and, but, therefore). Each binds two sentences with a different grammatical force — and each sits at a different point on the spectrum between a free pair (either sentence stands alone) and a tight bind (one sentence is ungrammatical without the other). Cohesion is the grammar that holds a text together; coherence is the meaning that results.