In architecture, a pattern of recurring elements, compositional strategies and holistic expressions is called a ‘style’ or ‘language’. Palladio’s architectural language, for example, uses classical elements (pilasters, pediments) composed in accordance with the principles of symmetry, proportion and harmony. Le Corbusier’s architectural language uses industrial elements (flat slabs, steel balustrades) arranged in geometric compositions to achieve a poetic, harmonious expression. Eisenman’s language is characterised by formal or structural abstraction, a deliberately anti-classical and anti-modernist expression. This chapter examines harmony and diversity in the architectural languages of Palladio, Le Corbusier and Eisenman. Focusing on design vocabularies and compositional strategies, the Chapter analyses twenty facades: five of Palladio’s country villas, five of Le Corbusier’s arts-and-crafts villas and five of his white purist villas, and finally, five of Eisenman’s abstract, numbered series of houses. The mathematical basis for the analysis is ‘perplexity’ (PP), which measures a language’s relative unpredictability. Two variations of perplexity are measured in this chapter. The first is ‘lexical perplexityLexical perplexity’, an indicator of the diversity of the vocabulary in a language, and the second is ‘semantic perplexitySemantic perplexity’, which suggests how the vocabulary is composed and expressed. Lexical and semantic properties have been linked to arguments about beauty in architecture.