1) US Dollar
Like most internationally traded commodities silver is priced in US dollars. At its most basic a decrease in the value of the US dollar relative to a commodity buyer’s currency means that the purchaser will need to spend less of their own currency to buy a given amount of the commodity. As the commodity becomes less expensive demand for the commodity rises, resulting in an increase in the price and vice versa.
As with gold but to a lesser extent, the value of silver, a fiat commodity currency, will also be largely determined by its attractiveness relative to other fiat currencies – the fiat paper currencies issued by central banks.