  During the last decades, many cognitive architectures (CAs) have been
realized adopting different assumptions about the organization and the
representation of their knowledge level. Some of them (e.g. SOAR [Laird
(2012)]) adopt a classical symbolic approach, some (e.g. LEABRA [O'Reilly and
Munakata (2000)]) are based on a purely connectionist model, while others (e.g.
CLARION [Sun (2006)] adopt a hybrid approach combining connectionist and
symbolic representational levels. Additionally, some attempts (e.g. biSOAR)
trying to extend the representational capacities of CAs by integrating
diagrammatical representations and reasoning are also available [Kurup and
Chandrasekaran (2007)]. In this paper we propose a reflection on the role that
Conceptual Spaces, a framework developed by Peter G\"ardenfors [G\"ardenfors
(2000)] more than fifteen years ago, can play in the current development of the
Knowledge Level in Cognitive Systems and Architectures. In particular, we claim
that Conceptual Spaces offer a lingua franca that allows to unify and
generalize many aspects of the symbolic, sub-symbolic and diagrammatic
approaches (by overcoming some of their typical problems) and to integrate them
on a common ground. In doing so we extend and detail some of the arguments
explored by G\"ardenfors [G\"ardenfors (1997)] for defending the need of a
conceptual, intermediate, representation level between the symbolic and the
sub-symbolic one.
