 Closely related to this issue to what extent use and design determine the function of an artifact is the problem of characterizing artifact kinds. It may seem that we use functions to classify artifacts: an object is a knife because it has the function of cutting, or more precisely, of enabling us to cut. On closer inspection, however, the link between function and kind-membership seems much less straightforward. The basic kinds in technology are, for example, ‘knife’, ‘aircraft’ and ‘piston’. The members of these kinds have been designed in order to be used to cut something with, to transport something through the air and to generate mechanical movement through thermodynamic expansion. However, one cannot create a particular kind of artifact just by designing something with the intention that it be used for some particular purpose: a member of the kind so created must actually be useful for that purpose. Despite innumerable design attempts and claims, the perpetual motion machine is not a kind of artifact. A kind like ‘knife’ is defined, therefore, not only by the intentions of the designers of its members that they each be useful for cutting but also by a shared operational principle known to these designers, and on which they based their design. This is, in a different setting, also defended by Thomasson, who in her characterization of what she in general calls an artifactual kind says that such a kind is defined by the designer’s intention to make something of that kind, by a substantive idea that the designer has of how this can be achieved, and by his or her largely successful achievement of it (Thomasson 2003, 2007). Qua sorts of kinds in which artifacts can be grouped, a distinction must therefore be made between a kind like ‘knife’ and a corresponding but different kind ‘cutter’. A ‘knife’ indicates a particular way a ‘cutter’ can be made. One can also cut, however, with a thread or line, a welding torch, a water jet, and undoubtedly by other sorts of means that have not yet been thought of. A ‘cutter’ would then refer to a truly functional kind. As such, it is subject to the conflict between use and design: one could mean by ‘cutter’ anything than can be used for cutting or anything that has been designed to be used for cutting, by the application of whatever operational principle, presently known or unknown.