 If we accept this three-fold classification, we can define our terms as follows: Impossibilism is the thesis that there are no free will worlds. Incompatibilism is the thesis that there are free will worlds but no deterministic world is a free will world. Compatibilism is the thesis that there are free will worlds and free will worlds include deterministic worlds. (For some objections to this three-fold classification see McKenna 2010 and Mickelson 2015a. For defense, see Vihvelin 2008 and 2013.)