The problem of being is central to Western metaphysics. Etched sharply in the verses of Parmenides, it took on distinctive colouring in Aristotle as the subject matter of a science expressly labelled ‘theological.’ For Aristotle, being could not be shared in generic fashion by other natures. As a nature it had to be found not in various species but in a primary instance only. The science specified by the primary nature was accordingly the one science that under the aspect of being treated universally of whatever is: it dealt with being qua being.