275It is not just the spatial envelope that is effective as a
screen, but also enclosures of various kinds, along with
thresholds, steps or boundary lines, that can be trans-
gressed. The screening of a > territory may be soft and flow-
ing, manifested for example solely through a gradual differ-
ence of levels, or through a subtle zoning effected through
light and shadow or change of material, and in extreme cases
even simply as a sonic or climatic island.
The principle architectural resource for screening, how-
ever, is the > wall with > openings. As closed, vertical planes,
walls are, first, obstacles to movement and perception; they
divide the space within which we find ourselves from an
external one, the space we occupy from an initially inacces-
sible one. Normally, that which we identify as a wall has a
rear side, and is thereby also related to a different space; by
means of this two-sidedness, it connects the two. In particular,
through an interplay with openings such as > doors and gates
or > windows, the wall expresses an ambivalence between di-
vision and connection. Depending upon construction and ma-
terials, various degrees of permeability to views, light, sound
or movement in various combinations modify its function as
communicative > filters.
On a scale of hermetic > closure to extensive openness,
the requirements of separation – the need for shelter, for ex-
ample from inclement weather, light or noise, and the secur-
ing of privacy or defence – are balanced against those for con-
nection – i.e. the desire for views to the outside, contact, and
opportunities for self-display. The double function of division
and connection served by screening, finally, makes possible
a scenic or voyeuristic interplay between concealment and
self-presentation, of withdrawal and self-display (> scene). In
many cases, objects or individuals that remain only partially
visible or only vaguely suggested behind a screening wall are
imbued with the appeal of the hidden. Their emergence into
visibility through the permeability or opening in the wall be-
comes an active unveiling or an > entrance that is supported