It also presupposes the means to protect that freedom, such as the protection of property rights and the enforcement of contracts. For there to be a single market, there must be a legislative body that establishes the rules and a judiciary that can enforce them. If there is a legislative and a judiciary, there has to be an executive arm to implement their decisions.
For a market to function, the three branches of government have to exist. This makes the single market a political union. What is not yet entirely clear in the case of the euro area, and apart from the ECB which has a clear but limited mandate, is who exactly will execute these powers, and to whom it will be accountable.