It was the spirit animating the mass and flowing from it, and it expressed the individuality of the building.

Louis Henry Sullivanwas an American architect, and has been called a “father of skyscrapers” and “father of modernism.” He was an influential architect of the Chicago School, a mentor to Frank Lloyd Wright, and an inspiration to the Chicago group of architects who have come to be known as the Prairie School. Along with Wright and Henry Hobson Richardson, Sullivan is one of “the recognized trinity of American architecture.” The phrase “form follows function” is attributed to him, although the idea was theorised by Viollet le Duc who considered that structure and function in architecture should be the sole determinants of form.