الفهرس 
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Abstract
Recognising coherent structure of a text is an essential task in natural language understanding. It is necessary, for example, to resolve anaphora, ellipsis, and ambiguity. One of the dominant factors of coherence of the text structure is lexical cohesion, namely the dependency relationship between words based on associative relations in common knowledge.
This thesis proposes an objective method for measuring lexical cohesion, especially semantic relations, between words. In this thesis, the researcher discusses how to apply the analysis of lexical cohesion in texts to the problem of evaluating text coherence.
In this work, we have two goals; one is to investigate the problem of lexical cohesion as an indicator of text coherence. The other is to increase our knowledge about cohesion in general, which is an interesting research area in its own right. The researcher starts with a specific point of view, considering cohesion and coherence as separate but related phenomena. Coherence is concerned with what makes sense in an utterance. Therefore, the semantics of discourse is the most important aspect of text from the coherence point of view.
Cohesion, on the other hand, is concerned mainly with how various parts of the text fit together, independent of semantics or discourse. In other words, the contents are less important than the links between text constituents. Cohesion plays an important supporting role for coherence. When two text constituents make sense together, that is, when they are coherent, they always have cohesive ties in common. One such a tie is lexical. Hence, lexical cohesion usually appears when coherence is present.
According to Halliday and Hasan (1976), there are five major classes of cohesive ties, some of which are realised through grammar and others through vocabulary. The latter is the main concern of this study which focuses on lexical cohesion.
Lexical cohesion is said to be the cohesive effect realised by the selection of vocabulary and it helps in connecting unrelated structures into a coherent whole. It is described as a problematic type of cohesion mainly because it deals with ‘open’ rather than ‘closed’ class items. The former includes lexical words which are unlimited in number and are subject to what linguists term ‘diachronic change’, such as nouns, verbs, adjectives, and adverbs.
Unlike grammatical cohesion, lexical cohesion makes use of semantic information to choose a proper replacement for an item. It also differs in that it “regularly leaps over a number of sentences to pick up an element that has not figured in the intervening text” (Halliday and Hasan, 1976). Consequently, Halliday in 1985 claims that “lexical cohesion may be maintained over long passages by the presence of keywords, words having special significance for the meaning of the particular text”.
As for the purpose of the study, it is threefold:
1. not enough work has been done in this field, especially in Egypt.
2. it contributes towards a better understanding of one aspect of text structure, namely lexical semantics.
3. it examines a number of passages from Lewis Carroll’s: Alice’s Adventures in Wonderland that have not received much attention from the critics so far, or that were only analyzed from a literary perspective. It shows that certain utterances may receive different interpretations depending on the scope context.
To achieve this aim, sample passages are taken from the story to indicate how lexico-semantic cohesive relations between words are created. Therefore, the more a lexico-semantic form is frequent, the more it is cohesive, and the more it is cohesive the more significant it is to the theme of the text.
The overall findings are: 1) all types of lexical cohesive devices that have been studied were used by the writer, which leads to a coherent text; 2) the ranking of the frequency of use of the different lexical cohesive devices is as follows, in a descending order: repetitions, followed by collocations, antonyms, synonyms, hyponyms, meronyms and homonyms with polysems being the least.
The thesis therefore provides important new research within the field of linguistics on how a representation of the cohesion of a text provides an understanding of the coherence of that text.