 An interesting example of fusion appears in Schurz 1991, when an alethic-deontic logic is defined by fusing a pure alethic logic with a pure deontic logic. This combination is used to analyze Hume’s ‘is-ought thesis’ (see  section 1  above) in formal terms. Other intuitively appealing examples of fusion are given in the pioneering paper Fitting 1969 by M. Fitting, where alethic and deontic modalities are fused (before the concept of fusion had ever been introduced).