The originator of Neoplatonism, Plotinus (204 - 270 CE), is sometimes described as the last great pagan philosopher. Early in his life he had studied various religions and philosophies, finding most of them inadequate for the Platonic mind (such as Scepticism, Stoicism, and Gnosticism).
He wrote doctrines of almost religious fervor based upon the One (or the Good), the highest being and ultimate cause of all things. The One is at the top of a hierarchy of principles or hypostases: the One, the Intellect, and the Soul. These principles are divided from the sensible world, and in fact a fundamental dichotomy between the intelligible and the sensible is the basis of Plotinus’ work. As the sum of an object is more than its parts, the unity of the everyday world is evidence of a higher level of being. This sort of upward movement through a hierarchy from the sensible, everyday world to higher planes is reminiscent of Plato’s theories of ascent as described in the Symposium and Republic.
The One creates the other levels through emanation, in which the cause remains unaffected, but by simply existing results in a flowing procession of descending stages of itself, much like light or heat. Any attempt to grasp it with the rational mind will fail, since Intellect itself presupposes multiplicity: a thinker and an object known. Even to say that the One is is to assign it a property, suggesting multiplicity.
The Intellect, the stage after the unified One, is the realm of Plato’s Forms, which are the thoughts of the Intellect itself. Free from the restraints of space and time, it is a purely contemplative level of the Forms, where subject and object of perception identify with each other.
The Soul is the third of the hypostases, the level below Intellect. The World-Soul, which Plotinus identifies with Plato's demiurge from Timaeus, is the link between the intelligible and the phenomenal world. The Soul is present entirely in each living body without being divided, in fact that the body is actually part of the Soul, illuminated by its presence within.
Finally, the matter of the sensible world is at the base of the hierarchy, and is not even considered to be a principle of being. Matter, as the stuff from which bodies are made, is the receptacle of Form, and embodies complete non-being and potentiality. Similarly, Plotinus’ idea of evil is one of privation, complete non-being: the opposite of Good, or the One. Human beings, according to Plotinus, possess a rational, immortal soul as well as a material body, and so exist at the boundary between the Intellectual and sensible realms. We are free to choose which direction in which to develop; developing one’s own intellectual illumination is not an imperative. For those who do choose the Intellectual realm, philosophy is the tool of purification and ascent, and in extreme cases, in transcending the Intellect itself one may arrive at a mystical, indescribable union with the One. According to Porphyry, Plotinus is said to have attained this union with the Absolute four times in his life, and indeed, much of his philosophy is based upon his own mystical experiences.