The term causality describes a relationship that exists between two or more things where a change in one thing - or set of things - causes a change in another. The essence of causality is a phenomenon being dependent on some other effect. As such causality is a connection or linkage between states or events through which one thing - the cause - under certain conditions gives rise to or causes something else - the effect. Causality forms a fundamental and pervasive part of our perception and interpretation of the world around us. Equally, our ability to act in the world depends on our grasp of causal relationships among things; the ways they act and interact. In everyday life humans - and other animals - rely on the assumptions of causality literally every waking second; in academia, much of science is the study of systematic cause and effect relations.