In the philosophy of Yoga, derived from the Samkhya system, all matter in the universe is reducible to one primary substance called Prakriti. Prakriti literally means the original power of action. It does not refer to substance in the physical sense but to the potential from which all forms of matter, energy and mind can arise. Prakriti is the original state of pure potential out of which all things become possible. Prakriti is the latent state of substance, like the seed that holds the potential for a great tree. It is the prima materia of the world of which matter, energy and mind are manifestations. Prakriti, we could say, is the causal or original form of all substances, from which their subtle and gross forms arise. It is extremely subtle, ethereal and transcendent, forming the basis for space that is its first material form.