Many attempts to characterise NP GA (non-topic subject) and NP WA (topic subject) have been made in the past. Some have examined their syntactic properties, some their semantic nature and others their discourse functions. None of these however, capture what native speakers understand by NP GA and NP WA, or properly reflect the intuition native speakers have for these items. Another major failure of past analyses is that the differential process employed by native speakers when choosing between

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... he two particles of GA and WA in a certain text or context has not been seriously studied. The assumption seems to have been that once NP GA or NP WA is somehow characterised, selection between the two is automatic, but as shown in this work, this is not the case. The research herein was undertaken firstly, in order to pursue or extract the essential or real differences between NP GA and NP WA as understood by native speakers; and secondly, to find out how the selection of one particle over the other is carried out in a real situation, e.g., in an actual text. Two major claims are made as the result of this investigation. Firstly, it is claimed that NP GA and NP WA can be described as denoting the concepts of existential assertion and existential presupposition respectively, and also that various syntactic as well as pragmatic phenomena concerning NP GA and NP WA can be accounted for by such fundamental semantic differences of NP GA and NP WA. Secondly, this dissertation claims that there are three selectional patterns concerning the use of GA and WA. The first one is where there is no conflict among the differential factors for selection, and the second is where conflicting factors are resolved by the ranking of the factors. The first and the second patterns are thus rule-governed, i.e., the appropriate particle may be predicted by a set of rules. The third case consists of situations in which native speakers are free to disagree with one another. The choice of particles here is not decided by rules but because of semanti [...]