 Sensibilia, as postulated entities, are particulars that become sense data when a perceiver enters into a relation of acquaintance with one of them. Thus, there are many potential trapezoidal appearances as of a table. When someone has a sequence of table-like experiences, some of those trapezoidal appearances are manifest as sense data. At other perspectives, not occupied by any observer, there are unsensed particulars. As Russell put it: