This book is a summary of the teachings of the great Neoplatonic philosopher Plotinus and deals with the nature of incorporeal principles in the realm of Mind or Spirit. Porphyry shows how the realm of Mind, because it is nowhere, not being limited by time or space, is present everywhere --- as Michael Hornum notes in his introduction, "Our higher self does not lie within us, as if an internal organ, or hover somewhere about the galaxy, but is present to each of us with an intimacy closer than any corporeal thing can have." Both Porphyry's text and Hornum's introduction invite the reader, in the words of Plotinus, "to wake to another mode of seeing, which every man has but few men use."