A number of authors argue that while species are evolutionary units, individuals and real entities, higher taxa are not. I argue that drawing the divide between species and higher taxa along such lines has not been successful. Common conceptions of evolutionary units either include or exclude both types of taxa. Most species, like all higher taxa, are not individuals, but historical entities. Furthermore, higher taxa are neither more nor less real than species. None of this implies that there is no (...) distinction between species and higher taxa; the point is that such a distinction is more subtle than many authors have claimed. (shrink)

Our topic is the ontology and persistence conditions of material objects. One widely held doctrine is that identity-over-time has causal commitments. Another is that identity-over-time is just identity as it relates one object that exists at two times. We believe that a tension exists between these two apparently sensible positions: very roughly, if identity is the primary conceptual component of identity-over-time and—as is plausible—identity is noncausal, then the conceptual origins of the causal commitments of identity-over-time become a mystery. We will (...) begin by formulating the two widely held doctrines and our puzzle more fully and more carefully. Then, the remainder of the paper will be devoted to analyzing views one might adopt that could minimize the tension. (shrink)

If a spinning sphere casts a shadow, does the shadow also spin? This riddle is the point of departure for an investigation into the nature of shadow movement. A general theory of motion will encompass all moving things, not just physical objects. Ultimately, I argue that round shadows do indeed spin. Shadows are followers of the objects that cast them. Parts of the shadow correspond to parts of the leader, so motion of the caster's parts accounts for motions of the (...) shadow's parts. I conclude with a discussion of how the dynamic aspects of shadows impose subtle constraints on other puzzles about shadows. (shrink)