Full Idea
I contend that the best available evidence suggests that for each category of objects an individual typically has several concepts. For instance, instead of having a single concept of dog, an individual has in fact several concepts of dog.
Gist of Idea
For each category of objects (such as 'dog') an individual seems to have several concepts
Source
Edouard Machery (Doing Without Concepts [2009], 3)
Book Reference
Machery,Edouard: 'Doing Without Concepts' [OUP 2009], p.52
A Reaction
Machery's book is a sustained defence of this hypothesis, with lots of examples from psychology. Any attempt by philosophers to give a neat and tidy account of categorisation looks doomed.