Two stages of skill development are: declarative (facts are interpreted) and procedural (knowledge is embodied in skill procedures). Knowledge compilation moves skills from the declarative to procedural stage in subprocesses of composition, which collapses sequences of productions into single productions, and proceduralization, which embeds…

The author analyzes some recent developments in the debate over the status of mental imagery. He attempts to specify what a propositional theory is, and considers arguments for and against the imagery position, i.e., whether visual imagery is encoded in terms of properties that are quite spatial and modality specific. (Author/RK)