In order for collection of sentences and utterances to succed effectively, the discourse needs to be organised or conducted in such a way that it will be successful. In written English this calls for both coherence and cohesion. For a text to be coherent, it needs to be in the right order. (…)

      No matter how coherent a text is, however, it will not work unless it has internal cohesion. The elements in that text must cohere or stick to each other successfully to help us navigate our way around the stretch of discourse. One way of achieving this is through lexical cohesion, and a way of ensuring lexical cohesion is through the repetition of words and phrases. (…) We can also use interrelated words and meanings to bind a text together (…)

      Another similar cohesive technique is that of substitution, using a phrase to refer to something we have already written. (…) Writers also use linkers such as and, also, moreover (…)

      These features are also present in spoken language, which also shows many examples of ellipsis (where words from a written-grammar version of an utterance are left out without compromising the meaning of what is said). (…)

                      (Harmer, J. The practice of English language teaching. 2007. Adapted)