A term for systems that are not well-founded, meaning that they are not based strictly on a few independent principles.

This means that they have looser logical requirements: that they are merely self-consistent. These systems are very important in computer science despite appearances, since many types are non-wellfounded in nature, such as stream types or other iterative (non-recursive) types. Also, whole-system analyses usually rely on this perspective implicitly, since bootstrapping is otherwise not easily expressible.

The difference can be summarized as "allowing anything that is not self-contradictory or explicitly disallowed" versus "allowing only the enumerated things and nothing else".

This page is linked from: Duality