Full Idea
Language does not appear to be necessary for forming categories, since prelinguistic infants acquire many categories, and even use categories to form inferences about unknown properties.
Gist of Idea
Prelinguistic infants acquire and use many categories
Source
Susan A. Gelman (The Essential Child [2003], 08 'Intro')
Book Reference
Gelman,Susan A.: 'The Essential Child' [OUP 2005], p.179
A Reaction
She cites lots of research in support of this claim. The idea may come as a surprise to some people, but not to me. I take it that categorisation is what a brain is for, including animal brains.