a market is free when an individual 1) may own property*, and 2) define any price they wish for their property, and 3) externalizes zero costs per transaction

the third condition recognizes how others can become imprisoned by the costs externalized by an individual, thus forming a type of transfer payment to those who avoid accepting full account of the cost of their production or consumption (failing to fulfill the terms of a previously-agreed-upon contract, included)

systemaccounting maintains a scientific definition for transactions occurring in a free market (w):

let,

t = time in seconds

a = value freely defined by a seller

b = value freely defined by a buyer

therefore,

w = value transacted between a buyer & a seller in free market (where a = b @ t)

see pricing & capitalism for details

*note: labor and access are forms of property