Since no one agency can control or regulate the myriad of transactions that occur (apart from blocking some trade here, and permitting it there), the whole of production falls under the sway of the law of value, and economics becomes a science aiming to understand "market behaviour", i.e. the aggregate effects of a multitude of people interacting in markets. How quantities of use-values are allocated in a market economy depends mainly on their exchange value, and this allocation is mediated by the "cash nexus".