Full Idea
For an ostension to be successful it is surely not necessary that I gather what sort of object it is you have indicated, such as being a horse or a zebra. I may even gather which thing you have indicated without knowing that it is a mammal or even alive.
Clarification
An 'ostension' is an act of pointing out
Gist of Idea
An act of ostension doesn't seem to need a 'sort' of thing, even of a very broad kind
Source
Richard Cartwright (Some Remarks on Essentialism [1968], p.157)
Book Reference
Cartwright,Richard: 'Philosophical Essays' [MIT 1987], p.157
A Reaction
This nicely articulates the objection I have always felt to Geach's relative identity. 'Oh my God, what the hell is THAT???' is probably going to be a successful act of verbal reference, even while explicitly denying all knowledge of sortals.