Any meaning to the term before 1892 would have been meaningless since before this date the term did not exist in the architectural vocabulary. The use of the word is closely connected with the evolution of modernism, so much so that it can speak, as Adrian Forty emphasizes, as a "triad of the modern movement" where space, together with form and design, finds its place. Modern architecture, in fact, in addition to representing a new approach to architectural matter also from a constructive point of view, has also represented a completely new way of talking about architecture by introducing the use of metaphors and specific terms in a specific vocabulary where words exist in relation to the others. Speaking of space at the time of the Pantheon of Agrippa, for instance, would have made no sense because no one would have understood the Pantheon in spatial terms. Talking about the 'Pantheon's spatiality' would have had no meaning for all those who had put hand to the construction of the building. In fact, we did not work with the space but with modules and the 'empty space' did not exist, because the whole void was occupied by a modular grid where everything found its commensurate, to quote Vitruvius, or like Greek used to say: its symmetry. This linguistic lack is very complicated, it will not be the purpose of this thesis to shed light on this topic because other people already dealt with, but it is important to make some clarifications because the way of talking about architecture and above all communicating it to whoever is or is not of the profession, is at the center of this scripts.

The architectural space originates from the 19th century German debate and it was the German architect and theorist Gottfried Semper who defined before anyone else the term space as the main theme of modern architecture. Semper argues that the first impulse of architecture is that of circumscribing space, a theory probably derived from Hegel for which circumscribe is a function of architecture. This theory was the source of conception of space for many German architects including, to make an instance known to all, Adolf Loos, who in his article The Principle of Cladding, 1898 states, in the footsteps of Semper, that "the architect's general task is to provide a habitable and welcoming space" and that "the effects are produced both by the materials and the shape of the space ". Remember, for instance, the observation of Adolf Hildebrand, destined to change the whole conception of the form in architecture (another modernist term), that in architecture the form is the space and must be first identified through spatial experience. This conception of the term is perhaps the closest to what we have today, according to which the meaning of architecture does not lie in the matter of the solid elements that compose it, but in the space that these elements define it. It is therefore essential to spend a few words on the elements that an architect has at his disposal to define a physical space, that is to define that volume of air delimited by walls, roof and floor, in short, a simple room. These elements belong to two categories; the category of opaque elements (walls, whether perimeter or partition) and that of transparent elements (identified in glazed elements or a void).

All this may seem trivial, but a wall on a plant is an indelible sign that has the function of clearly separating two environments; take for instance the layout of a hotel, two people sleep in rooms with beds resting on the border wall that are actually ten centimeters apart from each other, but despite this they perceive their room as intimate and private. If an opaque element has a closing effect, a transparent element produces the exact opposite effect and, in the case of a glazed wall, the perceived space extends beyond the physical limits of the building, stretching to infinity. In addition to the opaque-transparent combination also the furniture and the materials with the relative chromatic scale influence the spatial experience; for instance, by inserting fixed furniture elements, the circulation inside the room is influenced, a room with black walls produces a different psychological effect compared to the same room with white walls and so on. Today with the advent of technology and the introduction of new materials and technologies, it is possible to talk about the concept of flexibility according to which in architecture it is possible not to define the exact function of the spaces, making sure that an element can perform more than one function; think about the Neoplasticism icon Schroder house made by Gerrit Rietveld in Utrecht, built in 1924, where mobile walls are used to define the spaces on the upper floor that are constantly changing. We realize how the architect has in his hands a power that can be controlled by the behavioral habits of the user and this influence becomes even stronger if this faculty extends from the individual buildings to a larger and therefore urban scale.

The considerations regarding the space intended as delimitation mentioned above, are applied by the Viennese architect, also of German language and disciple of Semper, Camillo Sitte, who considers the urban design "art of space" and where other architects considered the delimiting the space thinking of the interior, Sitte adapted this theme to the outer space. In this way, the opposition of positive and negative spaces can be introduced, where positive space means buildings and with negative space the air left free between buildings in order to create squares, parks and streets. The question then arises spontaneously: since space is something extremely complex that holds more elements linked, be they psychological, physical, material and so on, how is it possible to communicate this experience? Plants, elevations, sections, axonometrías, three-dimensional models are able to communicate correctly the pure spatial essence without losing that infinite number of information that are created during the construction process? Are these the only tools that an architect/engineer has or exists of the other that can completely upset the current way of communicating architecture, focusing precisely on the spatial dimension? This is what we will try to understand in these pages where space experience is at the center of our interest.