The particular subject of this article is the very first sentence of Aristotle’s Metaphysics book Lambda: what does it really mean? I would stick to the most generous sense: (Aristotelian) theoria is about substance. Indeed, it has been often held that Lambda ignores the so-called focal meaning, and shows a remarkably rough stage of Aristotle’s conception of prime philosophy. By contrast, in this light, the very incipit of Lambda appears to testify Aristotle’s concern in an ontological foundation of theoretical wisdom (...) as such, which Lambda shares with the Metaphysics “central books”, Zeta in particular, in a not less coherent and possibly more advanced form. (shrink)