have that effect. But that appears to be a desirable consequence of the rule rather than its main objective. The person to be joined must be one whose presence is necessary as a party. What makes a person a necessary party is not merely that he has relevant evidence to give on some of the questions involved; that would only make him a necessary witness. It is not merely that he has an interest in the correct solution of some question involved and has thought of relevant arguments to advance. The only reason which makes it necessary to make a person a party to an action is so that he should be bound by the result of the action and the question to be settled, therefore, must be a question in the action which cannot be effectually and completely settled unless he is a party. The line has been drawn on a wider construction of the rule between the direct interest or the legal interest and commercial interest. It is, therefore, necessary that the person must be directly or legally interested in the action in the answer, i.e. he can say that the litigation may lead to a result which will affect him legally that is by curtailing his legal rights. It is difficult to say that the rule contemplates joining as a defendant a person whose only object is to prosecute his own cause of action. Similar provision was considered in Amon v. Raphael Tuck & Sons Ltd., wherein after quoting the observations of Wynn-Parry, J. in Dollfus Mieg et Compagnie S.A. v. Bank of England, that their true test lies not so much in an analysis of what are the constituents of the Applicants’ rights, but rather in what would be the result on the subject matter of the action if those rights could be established, Devlin, J. has stated :
