1) Weak Emergence:
Describes a model of a system’s behaviour.
Consider the example of a flock of birds to the left. The V-shape is a physical property that emerges that allows a set of birds to migrate with less expenditure of energy than if they migrated by themselves. From simple behavioural interactions whereby a bird chooses a flight path based on the vortices generated by its flockmates, the shape of a "V" naturally emerges, even though (it seems) that no single bird was by itself striving to create a V-shaped flock. We dub this "weak" emergence because the flock shape is a physical property that is directly traceable to the physical properties of the birds' individual positions. Biomolecules could be cited as examples of systems which display weak emergent properties because their emergent structure physical and directly traceable physical properties of their constituent parts.