At conceptual and linguistic levels of cognition, events are said to be represented in terms of abstract categories, for example, the sentence "Jackie cut the bagel with a knife" encodes the categories Agent (i.e., "Jackie") and Patient (i.e., "the bagel"). In this paper, we ask whether entities such as "the knife" are also represented in terms of such a category (often labeled "Instrument") and, if so, whether this category has a prototype structure. We hypothesized the Proto-instrument is a "tool": a physical object manipulated by an intentional agent to affect a change in another individual or object. To test this, we asked speakers of English, Dutch, and German to complete an event description task and a sentence acceptability judgment task in which events were viewed with more or less prototypical instruments. We found broad similarities in how English, Dutch, and German partition the semantic space of instrumental events, suggesting there is a shared concept of the Instrument category. However, there was no evidence to support the specific hypothesis that tools are the core of the Instrument category--instead, our results suggest the most prototypical Instrument is the direct extension of an intentional agent. This paper supports theoretical frameworks where thematic roles are analyzed in terms of prototypes and suggests new avenues of research on how instrumental category structure differs across linguistic and conceptual domains.