The term ‘emergence’ often causes confusion in science and philosophy, as it is used to express at least two quite different concepts. We can label these concepts _strong_ _emergence_ and _weak emergence_. Both of these concepts are important, but it is vital to keep them separate.

The objective probability of every physical event is fixed by prior physical events and laws alone. (This thesis is sometimes expressed in terms of explanation: In tracing the causal history of any physical event, one need not advert to any non-physical events or laws. To the extent that there is any explanation available for a physical event, there is a complete explanation available couched entirely in physical vocabulary. We prefer the probability formulation, as it should be acceptable to any physicalist, (...) though some reject the explanation formulation.) (3) Causal Exclusion. (shrink)

A framework for representing a specific kind of emergent property instance is given. A solution to a generalized version of the exclusion argument is then provided and it is shown that upwards and downwards causation is unproblematical for that kind of emergence. One real example of this kind of emergence is briefly described and the suggestion made that emergence may be more common than current opinions allow.