The One Is All Things and Know One of Them

The one is supposedly the source of all things, but if it is utterly and completely one, how does it generate something multiple? Later authors wondering about this aspect of neoplatonism invoke the so-called ex-uno-unum principle. Plotinus doesn't explicitly endorse a principle along these lines, he clearly sees it as an important challenge to explain how multiplicity can arise from unity. The puzzling thing here, if there's only one puzzling thing, is why this should give rise to the forms.