Their underlying principles are derived from the law of agency and not from the law of partnership. Yet they are true associations and cannot properly be classified with the trusts and the joint contractual relations already considered. Because they are true associations and frequently have to do with commercial rather than social affairs it is not always easy to distinguish them from partnerships. An illustration of this is the stock exchange, a mighty factor in big business. Its members are actively engaged in business for profit under the auspices of the exchange, but it is their individual business and not that of the association. The Law Of Unincorporations and Similar Relations by Sydney R. Wrightington, Boston—Little, Brown, and Company (1916)