 How to respond to the sufficiency problem? Some respond by denying the coherence of the position that causes the problem. Necessitation dualism as we have just described it violates (what is known as) Hume’s dictum that there are no necessary connections between distinct existences. According to necessitation dualism, mental and physical properties are metaphysically distinct, and yet are necessarily connected. However, Hume’s dictum is itself a matter of controversy (see Jackson 1993, Stalnaker 1996, Stoljar 2010, and Wilson 2005, 2010). Another approach appeals to a priori physicalism which will examine below (see Jackson 2006). But by far the most common response has been to concede that the sufficiency problem shows that supervenience formulation of physicalism is too weak (e.g. Kim 1998), and to look for an alternative. 