First defined by George Henry Lewes in "The Problems of Life and Mind". According to Lewes: "Although each effect is resulting from its components, the product of its factors, we cannot always plot the process steps, to the point of seeing in the product the mode of operation of each factor. In this case I propose to call this emerging effect. It arises from combined agents but in a way that does not expose the agents in action."

The mind, for example, is considered by many to be an emerging phenomenon as it arises from the interaction distributed between various neural processes (including also some of the body and environment) without being able to reduce itself to any of the components that participate in the process (none of the neurons separately are conscious).

The concept of emergency is hotly debated in science and philosophy because of its importance for the foundation of the sciences and the possibilities of reduction among them. It is equally crucial given the consequences and implications for the very perception of the human being and its place in nature (the concepts of free will, responsibility or consciousness depend, to a large extent, on the possibility of the emergency) . The concept of emergency has gained renewed strength in the wake of the rise of the sciences of complexity and plays a fundamental role in the philosophy of the mind and the philosophy of biology.