  It is now more than a half-century since the Physical Symbol Systems
Hypothesis (PSSH) was first articulated as an empirical hypothesis. More recent
evidence from work with neural networks and cognitive architectures has
weakened it, but it has not yet been replaced in any satisfactory manner. Based
on a rethinking of the nature of computational symbols -- as atoms or
placeholders -- and thus also of the systems in which they participate, a
hybrid approach is introduced that responds to these challenges while also
helping to bridge the gap between symbolic and neural approaches, resulting in
two new hypotheses, one that is to replace the PSSH and other focused more
directly on cognitive architectures.
