Emergence is currently used in both reductionist or "anti"-reductionist senses, being ambiguous the current expression " the whole is more than the sum of parts". It is clear the epistemological use of the term emergence. Entropy is an obvious example. A macroscopic description arises from a practical, statistical approach to study the behavior of a great number of particles. But is it ever so? For example, in the case of a cell or the mind, does emergence reflects only a limitation of our knowledge or rather express an ontological change?