 The appeal to unpredictability or other epistemic criteria plays a significant role in accounts of weak emergence (going all the way back to Broad’s [1925] highly influential discussion), even though the intended contrast with “reductionism” is ontological. It is near the surface in the non-aggregativity account of emergent autonomy summarized in  section 2.2.1  above, in which the non-linearity of macro-system dynamics (resulting in practical unpredictability) is taken to be a hallmark of (weak) emergence. Bedau (1997, 2010) proposes that we build this distinctive discovery of modern complex systems research into our theoretical elucidation of emergence. Specifically, a feature of or process within a macro-system is weakly emergent just in case it is derivable from the prior micro-facts leading up to it, but only in an informationally incompressible way: describing its macro-state at prior times by aggregating all of its underlying micro-states at those times and iterating their micro-dynamics. When a system’s macro-evolution is explanatorily incompressible in this way, it is not dynamically characterizable in fundamental physical terms: its distinctive evolutionary patterns are not foreshadowed in any way in the micro-evolutionary patterns.