It is well known what use was made of the part-whole notions in the metaphysics of Franz Brentano and his followers. They were preferred to the traditional metaphysical notions of genus-species, matter-form, substance-accident, etc. as intuitive, universal and, it seemed likely, clearer than the former ones.¹ The notions of part-whole, performing the main role in metaphysical analyses, subsequently were brought into focus themselves. The importance attached to them, common in Brentano's School, is evident in Twardowski's influential Habilitationsschrift ">Zur Lehre vom Inhalt und Gegenstand der Vorstellungen. The theoretical interest of these notions culminates in the third part of Edmund Husserl's Logical Investigations, Zur Lehre von den Ganzen und Teilen. Husserl, in his outline of a strict theory of parts and wholes, on the one hand proposes something better than the tentative statements of Twardowski, but on the other — very likely unconsciously — uncovers a certain essential difficulty contained in the whole attempt at "mereologising' metaphysics.