A text is cohesive when the elements are tied together and considered meaningful to the reader

ANALYSING COHESION
A text is cohesive when the elements are tied together and considered meaningful to the reader. Cohesion occurs when the interpretation of one item depends on the other, i.e. one item presupposes the other (Halliday & Hasan, 1976).
Cohesion in texts includes the use of connectives and conjunctions and more sophisticated texts effectively use a variety of referring words, substitutions, word associations and text connectives to improve the flow of the writing.
It refers to the use of linguistic devices to join sentences together, including conjunctions, reference words, substitution and lexical devices such as repetition of words (or synonyms), collocations and lexical groups. Students need to connect ideas in logical ways in order to display and build precise factual knowledge, develop their ideas to persuade more convincingly and express more complex relationships in their speech and writing.
Conjunctions and connectives are cohesive devices that work to improve the flow of the writing. Conjunctions operate within sentences and connectives relate to meaning between sentences. Different types of conjunctions are used to express different types of relationships between ideas.

Cohesion in discourse analysis refers to how all the elements of a text or work are linked together and work together to create meaning for the reader of the text. By examining the cohesion within a text, a reader can grasp the underlying structure and meaning of the work.

Theory of Cohesion Since the term of cohesion in paragraph refers to the content relationship, Michael Halliday and Ruquaiya hasan propose five cohesive devices in English (1976) as a mark of cohesion in discourse. Cohesion has role of building up sentences in any given text. This comes through the linking of different parts of a text to each other so that it gives a structure to a text. It helps in hanging sentences together in a logical way, for having a right meaning. So, cohesion has a relation with the broader concept of coherence. According to Halliday and Hasan (1976: 6) classify cohesion in English into two broad categories: grammatical cohesion and lexical cohesion. Grammatical cohesion is the surface marking of semantic link between clauses and sentences in written discourse and between utterances and turn in speech. Then, lexical cohesion refers to how the writer uses lexical items such as verb, adjectives, nouns and adverbs to relate to the text consistently to its area of focus (Eggins, 1994). It is signaled by means of lexical elements/vocabularies. Grammatical cohesion includes devices such as reference, substitution, ellipsis, and conjunction (Tanskanen, 2006: 15). Reference refers to items of language that instead of being interpreted semantically in their own right, make reference to other item for which the context is clear to both sender and receiver. In written text, reference indicates how the writer introduces participant and keeps track of them throughout the text. According to Halliday and Hasan, (1976:37) there are three main types of references: personal reference, demonstrative reference, and comparative reference. The category of personal reference includes: 1) personal pronouns, e.g I, me, you, him, she, he, her, we, us, they, them, it; 2) possessive determiners, e.g my, yours, their, its, our, his, her; 3) possessive pronouns, e.g. mine, yours, hers, theirs, ours. The categories of demonstrative reference include three classes namely: nominative demonstrative (this, that, these, those), circumstantial demonstrative (here, there, now, then) and definite article (the). The classify of comparative reference into two kinds, namely: “general” and “particular” comparison. General comparison deals with comparison which is simply in terms of likeness and unlikeness, without respect to any particular property: two things may be the same, similar or different (where “different” includes both “not the same” and “not similar”) According to Halliday and Hasan emphasize that substitution is a relation in the wording rather than in the meaning. They also explain that there are three types of substitution, namely: nominal (one/ones), verbal (do) and clausal (so, not) Ellipsis is omission of elements normally require by the grammar which the speaker/writer assumes as obvious from the context and therefore need not to be raise. Halliday and Hasan (1976: 146) clasify Ellipsis into three types; Nominal ellipsis, Verbal ellipsis, and Clausal ellipsis. Mather & Jaffe (2002: 1) state that conjunction represent semantic relation that expresses how a clause or statement is relate in meaning to a previous clause or statement; it is signal by a specific connecting word or phrase. Halliday and Hasan also classify conjunction into four types, namely adversative, additive, temporal and causal. According Halliday and Hasan (1976) divide lexical cohesion into two major categories, namely: reiteration and collocation. Reiteration is a mechanism of producing cohesion in a text by means of repetition of two or more lexical items that are observable at the surface of the text. The following is example of the use of reiteration which was quote from Halliday and Hasan (1976: 279) There is a boy climbing a tree a. The boy is going to fall if he doesn’t take care (repetition) b. The lad is going to fall if he doesn’t take care (synonym) c. The child is going to fall if he doesn’t take care (super ordinate) d. The idiot is going to fall if he doesn’t take care (general word) Collocation is achieved through the association of lexical item that regularly occur. It pertains to lexical items that are likely to be find together within the same lexical environment. The following is as the example: Plants characteristically synthesize complex organic substances from simple inorganic raw materials. In green plant, the energy of this process is sunlight. The plants can use this energy because they process the green pigment chlorophyll. Photosynthesis or light synthesis, is a self feeding, or autotrophic process (Pearson, 1987 in Nunan, 1993:28) In the text above it could be said that the following items are examples of lexical collocation because they all belong to the scientific field of biology:
Theory of Coherence The term ‘coherence’ is regarded as the link in a text that connects ideas and makes the flow of thoughts meaningful and clear for readers (Castro, 2004). The definition came from Halliday and Hasan’s (1976: 23) coherence refers to the elements internal to a text which consist of cohesion and register. Pearson, Roland & Speek, Barry Pennock (2005) states that coherence is an umbrella term for many aspects, such as the sequencing of events covered in the text, completeness of the actions or concept laid out in it and whether the text conforms to what we would expect from a piece of writing belonging to a given genre. Enkvist (1990) defines coherence as “the quality that makes a text conform to a consistent world picture and is therefore summaries able and interpretable” and coherence is primarily related to the nature and property of the text. Like Enkvist, Brown and Yule (1983) believe that coherence depends primarily on the interpretation of linguistic messages. Enkvist (1978) distinguishes between two types of semantic connection: (1) connection through cohesion in the surface level and (2) connection through coherence in the profound level.