An introductory chapter runs through "the contours of theoretical development", introducing the theorists from Vitruvius to Eisenman around which the book is centred. Hearn then covers some universal issues: the social status and education of architects, standards of judgement and justifications thereof, and the uses of the past.
Key figures before 1800 included Vitruvius, Alberti, Palladio, Serlio, and Michelangelo. Classical design was based on the columnar order of the peripteral temple, with key buildings as images of the ideal. Hearn explains the classical orders — Doric, Ionic, Corinthian, Tuscan — the modifications to them, and the return to purity. And he traces the development of an aesthetic based on the breaking of the rules, developed in reaction to the classical orders and going back to Vitruvius himself.
"For as long as the classical orders were the basis for architectural design, the use of rational proportion was one of the architect's key obligations."
"Expression in terms of conceptual principles rather than of regulatory conventions is the distinction that divides the architectural theory of the modern era from all that went before."
Key figures after 1800 included Viollet-le-Duc, Ruskin, Andrew Jackson, Frank Lloyd Wright, Sullivan, Le Corbusier, and Scheerbart. Themes and topics covered here include: rational design method and the use of metaphors (machines, organisms, crystals); generative planning and the design of private houses; "honest structure", "form follows function", and skyscrapers and the "high tech" movement; the use of materials and "truth to the medium"; the "vexed issue" of decoration and integrity of design; restoration (a 19th century innovation, extended in the 20th to ordinary buildings); and the design of cities.
A short final section covers theory since 1965: Venturi and the postmodern critique of modernism, Peter Eisenman and deconstructivism, and the use of computers and new directions in design method.
Almost no architectural background is assumed by Ideas That Shaped Buildings, though some concepts are never explained: "peripteral temple", for example, or "Gothic". (A short glossary might have been useful here; it's also frustrating that the index only covers names.) A novice to the area, I found Hearn's an enjoyable and informative introduction to architectural theory. The cyclic structure and the focus on leading theorists made it easier to find my feet, while the presentation brought the issues and debates to life without straying from the core ideas. A selection of plans and black and white halftones of buildings are also helpful.