Desktop computers capable of rendering high-fidelity, three-dimensional graphics have long been used for the development of virtual worlds. Typical interaction with virtual worlds occurs in fully immersive virtual reality systems that make use of complex spatial inputs, but such inputs are not easily replicated with a keyboard and mouse. We present the concept of avatar manipulation as a metaphor for interacting with virtual worlds on desktop computing hardware, and we explain the benefits of this metaphor over techniques that require knowledge of keyboard and mouse commands for interaction. Based on our ideas, we explain an example implementation of the concept that we have written called PySim, a plug-in to VR Juggler. We then review our implementation and propose improvements for future versions.

The meaning of the English adverb only has been the subject of intense debate; in particular, regarding the status of its prejacent. It has been argued that the latter is a presupposition, a conversational implicature, and an entailment. I argue that it is closer to a presupposition than to an entailment or a conversational implicature, but it may best be characterized as a non-speaker-oriented conventional implicature. The detailed consideration of the meaning of only sheds light on the relationship between these various types of meanings, contributing to the recent reconsideration in the literature of the nature of presuppositions and implicatures, both conversational and conventional.