Epiphenomenalism is a mind–body philosophy marked by the belief that basic physical events (sense organs, neural impulses, and muscle contractions) are causal with respect to mental events (thought, consciousness, and cognition). Mental events are viewed as completely dependent on physical functions and, as such, have no independent existence or causal efficacy; it is a mere appearance. Fear seems to make the heart beat faster; though, according to epiphenomenalism, the state of the nervous system causes the heart to beat faster. Because mental events are a kind of overflow that cannot cause anything physical, yet have non-physical properties, epiphenomenalism is viewed as a form of property dualism.