Full Idea
The categoricalist conception of properties takes them to be quiddities, which are primitive identities between fundamental qualities, having no difference with regard to their essence.
Gist of Idea
Categoricalists take properties to be quiddities, with no essential difference between them
Source
Alexander Bird (Nature's Metaphysics [2007], 4.5)
Book Reference
Bird,Alexander: 'Nature's Metaphysics' [OUP 2007], p.97
A Reaction
Compare 'haecceitism' about indentity of objects, though 'quidditism' sounds even less plausible. Bird attributes this view to Lewis and Armstrong, and makes it sound well daft.