Propositional objects discussed in Stuart Walker's book "The Spirit of Design" (Routledge-Earthscan, 2011) are available within the items entitled:
Design and Meaning at: http://imagination.lancs.ac.uk/articles/Design_and_Meaning
The Spirit of Design: objects, environment and meaning at: http://imagination.lancs.ac.uk/outcomes/Spirit_Design_objects_environmen...
Links to book:
Routledge website: http://www.routledge.com/books/details/9781849713641/
Amazon.co.uk website: http://www.amazon.co.uk/The-Spirit-Design-Objects-Environment/dp/1849713...