In architecture, form refers to a combination of external appearance, internal structure, and the unity of the design as a whole, an order created by the architect using space and mass.
Appearance
The external outline of a building includes its shape, size, color, and texture, as well as relational properties, like position, orientation, and visual inertia (appearance of concentration and stability).
Architects are primarily concerned with the shapes of the building itself (contours, silhouettes), its openings (doors and windows), and enclosing planes (floor, walls, ceiling).
Forms can have regular shape (stable, usually with an axis or plane of symmetry, like a triangle or pyramid), or irregular; the latter can sometimes be constructed by combining multiple forms (additive forms, composition) or removing one form from another (subtractive forms).
Multiple forms can be organized in different ways: in a line or along a circle; as a regular grid; as an irregular cluster; in a star-like radial pattern.
Structure From the architectural standpoint, the structure is what keeps the architectural construction as a solid body. It is a set of bulky objects that are pervasive throughout the building and thus are closely related to its shape. Historically, a form was expected to seamlessly and elegantly combine the artistic expression and physical reality in "a meeting of art and science through design".
Multiple approaches were suggested to address the reflection of the structure in the appearance of the architectural form. In the 19th-century Germany, Karl Friedrich Schinkel suggested that the structural elements shall remain visible in the forms to create a satisfying feeling of strength and security, while Karl Bötticher as part of his "tectonics" suggested splitting the design into a structural "core-form" () and decorative "art-form" (). Art-form was supposed to reflect the functionality of the core-form: for example, rounding and tapering of the column should suggest its load-bearing function. In the tectonics as envisioned by Bötticher, the function (defined as requirements for internal space) had driven the design: the size determined the roof technology to be used, the latter in turn mandated the support requirements, creating a structural outline of the building, architecture was an art of resolution of the conflicts between the functional need and architectural forms that can be built.
New materials had frequently inspired new forms. For example, the arrival of construction iron essentially created a set of new core-forms, and many architects got busy inventing the matching art-forms. Similarly, introduction of reinforced concrete, steel frame, and large plates of sheet glass in the 20th century caused creation of radically new space and mass arrangements. The properties of these materials enabled the Modern architecture to create a novel visual vocabulary that showcased the technology.
The shape of a form can make support structure for it more or less "efficient". Efficiency can be defined either as a ratio of the construction material used to the structural load supported, or as a minimal total cost of the building. Generally, a form that creates primarily compressive and tensile forces (as opposed to bending) in its support structure, requires significantly less material. On the cost side, this is balanced against the simplicity of the construction: for example, in the industrialized societies, with high-wage economies, the construction is dominated by material-inefficient, but low-cost beam and post (steel frame or concrete frame) structures. Thin concrete shell forms are remarkably efficient and aesthetically pleasing (cf. Riverside Museum or L'Oceanogràfic). However, some architects viewed concrete shells as a license to experiment with the arbitrary curvilinear shapes, producing few technically disastrous (although frequently iconic) buildings like the Sydney Opera House, where the visually appealing sail-like roof turned out impossible to build as designed and now hides a very heavy (and expensive) reinforced concrete networks actually carrying the load.
Space and mass
Space and mass (also mass and volume) are the primary ingredients that an architect uses to compose an architectural form. The essence of a building is the separation between the finite indoor space fit for humans and unrestricted natural environment outdoors. Unlike the physical objects manifesting the mass (for example, the floor, walls, and ceiling), the human experience of the void, air-filled indoor space is not obvious, yet the idea of architectural space is very old, going back at least to the (táxis, "order"), a subdivision of a building into parts.
The psychological effects of space are very common, as suggested by the English language: feeling of insecurity and compression in "confining circumstances" of inadequate space and powerful "elevated experience" of standing above a great expanse. Space and mass in architecture are not entirely separable: as was noted by George Berkeley in 1709, two-dimensional human vision cannot fully comprehend three-dimensional forms, so the perception of the space is a result of immediate visual sensation and the knowledge of textures pre-acquired through touching (this idea evolved in the 19th century into a theory of apperception).
By placing restrictions on the observer's movements, an architect can evoke a variety of emotions. For example, in Gothic architecture, an elongated nave suggests a forward movement towards the altar while the compressive effect of tall walls draws the gaze towards vaults and windows above, causing a feeling of release and "uplifting" experience. Renaissance architecture tries to guide the observer to a point where all the features appear to be in equilibrium, resolving the conflict between the compression and release, thus creating a feeling of being at rest. Neo-Palladianism in England paid attention to the architectural circulation, with the views unfolding as the visitor experiences the building.
The architectural use of space is not restricted to indoors, similar feelings can be recreated on a grand scale in the city landscape. For example, the colonnades of the St. Peter's Square in Rome suggest walking towards the entrance of the cathedral in a way similar to the navigation experiences indoors. At the same time, the facades of a standalone building usually do not create an architectural space, instead the outside of a building can be thought of as a kind of sculpture, with the masses arranged in a large void.
The balance between the space and mass varied with the historical period and function of the building. For example, Egyptian pyramids and stupas in India have practically no internal space, are almost all mass, and thus manifest themselves in a sculptural fashion. The Byzantine architecture, in contrast, offered in its churches an ascetic shell outside combined with sophisticated indoor spaces. Gothic cathedrals expressed the fusion between the secular and spiritual powers through an equilibrium between the worldly facade masses and mystic spaces inside. The relative importance of space and mass can change very quickly: in 1872, Viollet-le-Duc wrote his book, Entretiens sur l'architecture, completely avoiding the use of the word "space" in its modern meaning; just 20 years later August Schmarsow was declaring the primacy of , "forming the space".
Modern architecture, utilizing the steel frame, enabled space partitioning without any practical limits, transparent walls of architectural glass enable visual journeys into the boundless world behind them. At the same time modern materials reduced the contrast between the space and mass, primarily through the reduced mass of the walls.
Symbolism The form can be considered to have a direct symbolic value used for communication between the architect and the customer. In particular, most art historians agree that the triangular pediment in the Greco-Roman architecture is not just an imitation of an older roof construction, but a representation of the divine. This idea, first presented in the modern times by a little-known (except for his theories) architect Jean-Louis Viel de Saint-Maux in 1787, was hinted at by Cicero much earlier. Cicero also suggested that the utilitarian and symbolic meanings of the pediment are not necessarily contradictory: originally designed as part of the gabled roof to protect from the rain, the pediment had gradually acquired a religious value, so if a building was designed for heaven, where the rain does not fall, dignity would dictate to add a pediment on top of it.
The ability of architecture to represent the universe and the common association of a sphere with the cosmos caused an extensive use of spherical shapes since the early Roman construction (Varro's Aviary, 1st century BC).
Theories Multiple theories were suggested to explain the origination of forms. Gelernter considers them to be variations of five basic ideas: A form is defined by its function ("form follows function"). For a building to be "good", it should fulfill the functional requirements imposed by external physical, social, and symbolic needs (for example, a theater should have unobstructed view of the stage from the spectators' seats). Each set of functions corresponds to an ideal form (that can be latent and still waiting for a thoughtful architect to find it); A form is a product of the designer's creativity. An architect's intuition suggests a new form that eventually blossoms, this explains similarities between the buildings with disparate functions built by the same architect; A form is dictated by the prevailing set of attitudes shared by the society, the Zeitgeist ("Spirit of Age"). While expressing his individuality, an architect still unconsciously reflects the artistic tastes and values that are "in the air" at the time; A form is defined by the socioeconomic factors. Unlike the Spirit of Age theory, the externalities are more physical (e.g., methods of production and distribution). Architects live in a society and their works are influenced by the prevailing ideology (for example, Versailles represents societal hierarchy while Prairie buildings reflect the power of bourgeoisie); Architecture forms are timeless; the good ones cross the geographical, cultural, and temporal borders. For hundreds of years, these beliefs were embodied in The Five Orders of Architecture. According to the theory of types there are only few basic building forms, like basilica or atrium, with each generating multiple versions with stylistic differences (the basilica form can be traced from Roman court buildings to Romanesque and Gothic churches, all the way to the 20th century Environmental Education Center in the Liberty State Park, New Jersey).
Early theories of form As the nomadic cultures began to settle and desired to provide homes for their deities as well, they faced a fundamental challenge: "how would mortals ... know the kind of built environment that would please the gods?" The first answer was obvious: claim the divine origin of the architectural form, passed to architects by kings and priests. Architects, not having access to the original source, worked out the ways to scale buildings while keeping order through the use of symmetry, multiples and fractions of the basic module, proportions.