Full Idea
The word 'concrete' is often used as the negative of 'abstract', with the slightly odd consequence that desires and hallucinations are thereby classified as concrete.
Gist of Idea
If 'concrete' is the negative of 'abstract', that means desires and hallucinations are concrete
Source
Michael Potter (The Rise of Analytic Philosophy 1879-1930 [2020], 12 'Numb')
Book Reference
Potter,Michael: 'The Rise of Anaytic Philosophy 1879-1930' [Routledge 2020], p.82
A Reaction
There is also the even more baffling usage of 'abstract' for the most highly generalised mathematics, leaving lower levels as 'concrete'. I favour the use of 'generalised' wherever possible, rather than 'abstract'.