 Like Brentano had done, Twardowski distinguishes, with respect to material parts, metaphysical from physical and logical parts on the basis of a notion of dependence and  separability.[8]  However, differently from Brentano, Twardowski does not construe the notion of dependence in terms of existence of the objects involved. His notion of dependence needs also to be applicable to non-existing objects. Consequently, Twardowski construes the notion of dependence of the parts of an object in terms of modes of presentability of the parts of an object, i.e. as existence of the parts of the content of a presentation (which always exists). The inseparability of a part p1 from a part p2 of an object O is not construed in the sense that it is not possible for p1 to exist without p2 existing, but in the sense that in the content of the presentation of an object O the part that represents p1 cannot exist without the part that represents p2 existing, that is, both must be elements of the content of the presentation of the object O.