  In the last years the debate on complexity has been developing and developing
in transdisciplinary way to meet the need of explanation for highly organized
collective behaviors and sophisticated hierarchical arrangements in physical,
biological, cognitive and social systems. Unfortunately, no clear definition
has been reached, so complexity appears like an anti-reductionist paradigm in
search of a theory. In our short survey we aim to suggest a clarification in
relation to the notions of computational and intrinsic emergence, and to show
how the latter is deeply connected to the new Logical Openness Theory, an
original extension of Godel theorems to the model theory. The epistemological
scenario we are going to make use of is that of the theory of vision, a
particularly instructive one. Vision is an element of our primordial
relationship with the world;consequently it comes as no surprise that carefully
taking into consideration the processes of visual perception can lead us
straight to some significant questions useful to delineate a natural history of
knowledge. The common Greek etymological root of theory and vision sounds like
a metaphor pointing out the analogy between the modalities of vision and those
we use to see and build the world because them both can say us something about
the central role of the observer and the semantic complexity of cognitive
strategies.
