This thesis extends a view of human reasoning which emphasises a theory of interpretation in conditional reasoning. It extends work on Wason's (1968) 'selection task', using novel rules and contexts to explore the factors that control subject interpretations, which in turn is reflected in their performance.

After reviewing the work on conditional reasoning and particularly the interpretative framework of Stenning & van Lambalgen (in press), the thesis explores subjects' reasoning with rules that describe processes extended in time are explored in two experiments.

The most striking finding is that many subjects exhibit an unusual constant anaphor reading, even though the anaphors involved are tenses rather than pronouns. Results are explained in terms of the temporal constraints involved in the situation described.

The thesis, then uses novel 'information packaging' manipulations which use colour to emphasise different distinctions in Wason's original task. This manipulation provides evidence of where subjects' attention already rests. This is combined with a task that gathers data of subjects' interpretation of negation.

Results are consistent with the idea that although subjects in the standard task are focussed on the distinction between cases that fit the rule and ones that do not, there is evidence that emphasising the mapping of the antecedent/consequent onto back/front of the cards is sensitive to these manipulations.

The negation interpretation task reveals striking divergences between subjects' interpretations and the classical model assumed in the literature, and these differences are interpretable in terms of default logic.

A few conditions were originally designed as controls only to end up generating striking results of their own. Colour is used in the truth conditional semantics of the rules (black/white replaces number/letter or vowel/consonant) instead of being used as mere information packaging.

Sizable increases in 'classical competence' responses are observed and this is interpreted in terms of the non-hierarchical structure of the properties used.

The question then arises about what cues in the surface of rules are sufficient to cue subjects to adopt descriptive or deontic interpretations. Studies using LSA and a novel tensor network operating on a database of rules gathered from selection task literature show conclusively that this classification can be achieved purely on superficial features.

The different distribution of function words and full lexical items in the two kinds of rules is critical. This thesis concludes that it is possible to direct subject towards specific interpretations on the task through the use of various semantic manipulations that include but are not restricted to the ones observed in this work.

Issues including the resolving the anaphora in the problem, the hierarchy of the structure of properties and the negation of clauses clearly influence the interpretation subjects arrive at which in turn affects their reasoning and responses.