Alfred North Whitehead,
An enquiry concerning the principles of natural knowledge
(1925)
“ Material Objects. 56.1 A material object is essentially a material object of a certain definite sort; namely, we define sorts of material objects, which are sets of objects with certain definite peculiarities, and a material object is such because it is a member of one of these sorts. For example a piece of wood is a material object because it belongs to the class of wooden objects and because this class possesses the requisite peculiarities. ”
