Full Idea
There may be ad hoc categories, as when people think about the things to pack in a small suitcase for a trip abroad.
Gist of Idea
There may be ad hoc categories, such as the things to pack in your suitcase for a trip
Source
Edouard Machery (Doing Without Concepts [2009], 1.4.1)
Book Reference
Machery,Edouard: 'Doing Without Concepts' [OUP 2009], p.22
A Reaction
This seems to be obviously correct, though critics might say that 'category' is too grand a term for such a grouping.