Roberto Casati

Holes are a good example of the sort of entity that down-to-earth philosophers would be inclined to expel from their ontological inventory. In this work we argue instead in favor of their existence and explore the consequences of this liberality—odd as they might appear. We examine the ontology of holes, their geometry, their part-whole relations, their identity and their causal role, the ways we perceive them. We distinguish three basic kinds of holes: blind hollows, perforating tunnels, and internal cavities, treating these uniformly as immaterial bodies. We develop a morphology of holes, focusing on the way a hole can be filled, and then look at the main properties of the resulting conceptual framework: holes are parasitic upon the surfaces of their hosts; holes can move, fuse into each other, split; they can be born, develop, and die. Finally, we examine how some morphological features of holes are represented in perception, including the conditions whereby we have the impression that we see, feel, or even hear a hole. The book has over 150 pictures and is completed by a formal appendix, a section with puzzles and exercises, and a extensive annotated bibliography.

The so-called "virtual world" is often described with the help of metaphors derived from ordinary discourse on perception and action. This should not be surprising, since virtual objects were partly conceived on the basis of these metaphors. Yet, it is not a given that these metaphors are appropriate; one might need to begin using different concepts and eventually to invent new ones, more appropriate to the phenomena they describe. It might even happen, as I shall show, that these new concepts will themselves be used in situations described by the discourses on perception, action and social behaviour in a way that so far seems perfectly natural, but that, in turn, might reveal itself to be entirely inadequate. One could use these new metaphors, born as they are of new practices and new usages, for the reinterpretation of the non virtual world. The subject of this piece is the metaphysics of the book. I shall look at the way in which the Web frees it from our inadequate conception of it. This emancipation, strangely, seems to involve an economic liberation.

Some concepts, such as colour concepts or value concepts, seem to bear traces of the mind's own make-up. For instance, an extreme position would be that colours and values are not in the world at all, they instead are mere projections that tell us more about the users of response-dependent concepts than about the world they inhabit. But even setting aside such extreme views, a number of important philosophical and psychological questions remain open. What exactly is response-dependence, and does any concept have this feature? What is the appropriate metaphysics for properties represented by response-dependent concepts, and for these concepts themselves? What determines the extension of such properties? How are we to account for knowledge expressed in terms of response-dependent concepts? What mechanisms correctly explain the origins of response-dependent concepts, and their role in representation?