Function or 'functionalism' in architecture is the defining principle which in its simplest form states that a building or structure should be derived solely from the function it is intended to fulfill. Employed by pioneering modernist architects including Louis Sullivan and Le Corbusier, functionalism, stood alone as the cornerstone of their definitions of honest, pure, and beautiful structure. In Louis Sullivan's 'Kindergarten Chats and Other Writings' he exposes the true inter-correlations at work between function and form (structure): "I suppose if we call a building a form, then there should be a function, a purpose, a reason for each building, a definite explainable relation between the form, the development of each building, and the causes that bring it into that particular shape; and that the building, to be good architecture, must, first of all, clearly correspond with its function, must be its image as you would say." Functionalism as an architectural principle can be traced back as far to the Vetruvian principles of Greek and Roman structure. For Louis Sullivan as well as Le Corbusier form was a mere manifestation of functional principles including the practical considerations of use, material, and structure and not by a preconceived picture in the designer's mind. Born in 1856 Louis Sullivan, deemed by some to be the "father of modern architecture," is credited with the creation of a wide variety of structural masterpieces all of which subscribe to his archetypal description and notion that "form ever follows function". Implicitly connected to Sullivan's principle of functionalism was his description of an organic quality that as he states is the very basis of life itself. Taken from his essay "The Tall Office Building Artistically Considered," first published in Lippincott's, March 1896, Sullivan states, " It is the pervading law of all things organic, and inorganic, of all things physical and metaphysical, of all things human and superhuman, of all true manifestations of the head, of the heart and of the soul, that the life is recognizable in its expression, that form ever follows function. This it the law." Sullivan's mastery of modern structure includes the Auditorium Building, Chicago (1889), Wainwright Building, St. Louis (1890), Guaranty Building, Buffalo (1894), and the Carson Pirie Scott Store, Chicago (1890) among many others. When describing the tall office building Sullivan divided the practical conditions into five clearly stated elements: First, a story below ground (a basement) containing the inner-workings of the buildings power, heating, and lighting. Second, a ground floor devoted to establishments requiring a large area and ample spacing with great freedom of access. Third, a readily accessible second story by stairways. Fourth, an indefinite number of stacked stories mimicking the principle of the honeycomb of a beehive. Fifth and final is the attic to which Sullivan credited as purely physiological in nature, but from which he created extreme uniqueness and expressionism by way of the freedom it afforded him. Among his organic and functionalist theories Sullivan called for a suspension of inorganic ornamentation to which he described as appearing merely like it was "tacked" on. Though he often criticized this faulty ornamentation Sullivan espoused a functionally organic ornamentation which he found to be an organic flowing beauty from the structure within, much like the limb of a tree. Le Corbusier, born Charles-Edouard Jeanneret in 1887 shared similar principles concerning modern architecture and functionalism as Louis Sullivan. Taken from Le Corbusier’s Vers une architecture (Towards A New Architecture), 1923: "You employ stone, wood, and concrete, and with these materials you build houses and palaces: that is construction. Ingenuity is at work. But suddenly you touch my heart, you do me good. I am happy and I say: This is beautiful. That is Architecture." This quotation exemplifies Le Corbusier's notion of the architect as an artist. Some of his major buildings include Villa La Roche, Paris 1923, Pavillion de L'Espirit Nouveau, Paris 1924, Villa Savoye, Poissy-sur-Seine, France 1928, and Unité d'Habitation of Meaux, France 1957 among countless others. Le Corbusier developed and was acclaimed for his five points of architecture most notably depicted in the Villa Savoye and discussed in his Veers une architecture. His first point was lifting the bulk of the structure off the ground, supporting it by reinforced concrete stilts or "pilotis". By way of the concrete stilts Le Corbusier was able to incorporate his second and third ideas of a free facade and an open floor plan (resembling the work of Frank Lloyd Wright). His fourth point called for the incorporation of long strip or "ribbon" windows which would grant an unencumbered view of the surrounding yard. His fifth and final point was to employ a roof garden, replacing the natural land overtaken by the building. Acclaimed for his functionalism in modern architectural design LeCorbusier took one step further in his five step process in creating aesthetically beautiful structures and space saving techniques which extended to his implementation of urban housing and the development of the "Do-Mi-No" principle. Whether regarding Sullivan or Corbusier in their critical theories of architecture both insisted on beginning the process of design with an analysis of the building’s function and of the best technical means of meeting it. The emphasis on Functionalism in modern architecture thus implies a reunion of architecture and engineering, which undoubtedly became separate entities during the classical revivalist phases of the early 19th century. Functionalism of an organic nature flowed through the works of both of these acclaimed architectural masterminds as they transformed the definitions of modern structure which exist to this day.