According to Adrian Forty, the term "space" in relation to design was all but meaningless until the 1890s. At that time two schools began to develop. Viennese Gottfried Semper in 1880 developed an architectural theory based the idea that the first impulse of architecture was the enclosure of space. Camillo Sitte extended Semper's ideas to exterior spaces in his "City Planning According to Artistic Principles" (1889). Concurrently, Friedrich Nietzsche built on ideas from Kant which emphasized the experience of space as a force field generated by human movement and perception. Martin Heidegger would later contradict both of these schools. In his 1927 "Being and Time" and 1951 "Building, Dwelling, Thinking" he claimed that space was neither a construct of the mind nor a given, but was "that for which a room has been made" and was created by the object within a room rather than the room itself. Henri Lefebvre would call all of this into question, linking designers' notions of themselves as space-makers to a subservience to a dominant capitalist mode of production. He felt that the abstract space they had created had destroyed social space through alienation, separation, and a privileging of the eye.