This thesis is an exercise in theory with an empirical exercise. It deals with the traditional architectural ideas of 'composition' and 'parti', and applies a formal analytic approach to them. It takes a top-down approach to the notion of 'composition', which tries to reflect the way architects think, and looks at the 'parti' as the deep structure of the building, which is abstract, global, and capable of many realisations. As a case study, 19 houses of Mario Botta are analysed. The purpose of the empirical exercise is to explore how far it is possible to produce an analytic construction of the notion of 'parti'. It asks: are there formal top-down themes which underly the composition of the houses and have to do with their relational structure? After the description of the houses a formal analysis of the identified themes takes place. These formal top-down themes are defined as rules. A distinction is made between the nature of the rule, the degree of its realisation and the domains (mass, elevations, plan) of its realisation. Formal analysis, thus, measures properties of the mass, the elevations and the plan. What analysis shows is that the interrelations of the rules define the 'parti'. Three phases are identified in the development of the 'parti' of the houses which show an evolution of it from combinations to structure. A distinction between a short and a long genotype for order is thus made, as well as a distinction between the intension and the extension of the rule seen as a relation. In the last part the thesis explores what these findings suggest towards theory building as well as implications for further research by addressing the notion of relation and by defining two different types of interrelations.