Given the above, we would obviously counsel against the use of "fuel" and "waste", and terms such as "chemically fueled" as they have misleading connotations. We suggest that "substrate" and "product" (defined by the spontaneous direction of the reaction) and "chemically driven" respectively are more useful. Indeed, rather than being driven by some energetic property of a "fuel", the continuous directed motion of a molecular motor such as 6, and the maintenance of non-equilibrium steady states more generally, is achieved because of the free energy change associated with mass action; the flow of substrate to product. 13g