The Promoters Act imposes taxation on a "promoters taxable amount" which is defined in relation to a person or persons as meaning "an amount that is a promoters taxable amount under section 7 in relation to an eligible promoters class in which the person is, or the persons are, included": the 1982 Assessment Act, s. 3(1). The tax is imposed in an amount equal to the promoters taxable amount: Promoters Act, ss. 4 and 5. A promoters taxable amount exists where the criteria specified in pars (a) to (h) of s. 7(1) or s. 7(2) are met. The chief of those criteria are a purchase of shares in a company by a person or persons who, immediately after the purchase, is or are capable of controlling more than 90 per cent of the voting power of the company, the non-payment of ordinary company tax or undistributed profits tax due and payable by the company, the entry into an arrangement or transaction that resulted in the company being unable to pay to the Commissioner all the company tax due and payable by it and the discontinuance after the time of the last purchase of a business previously carried on by the company. A promoters taxable amount does not exceed the difference between the value of the net assets of the company immediately before the time of the last purchase and the sum of the amounts of purchase price of the shares and tax paid after the purchase but before 25 July 1982: s. 7(3). A promoters taxable amount may exist in relation to the persons in any of seven eligible promoters classes specified in s. 7(8), including the purchasers of the shares (par. (a)), their agents or brokers (par. (b)), and their associates who gave them financial assistance for the purpose of, or in connexion with, the purchase: par. (c). It was submitted that, as promoters recoupment tax was imposed upon those several classes in relation to whom a promoters taxable amount exists, the Promoters Act deals with more than one subject of taxation. Purchasers, agents, brokers and financiers are, in their several ways, involved in a purchase of shares in a company, but the activities which characterize their respective involvement and expose them to tax liability are different. Are those activities merely descriptive of the objects of the tax or do they identify different subjects of taxation? The question is not to be answered by analytical or logical classification but on "common understanding and general conceptions". The common criterion of the existence of a promoters taxable amount in relation to any person is his involvement, directly or indirectly, in the purchase of shares in a company which, as a result of some arrangement or transaction, becomes unable to pay the whole of the company tax that has become due. That common foundation of liability is a sufficient connexion among the several heads under which a person may be assessed to promoters recoupment tax to bring all heads within the same subject of taxation. The criteria to be found in s. 7 are not so diverse as to reveal that "very clear demonstration of error" which Isaacs J. thought the Court should perceive before holding that the Act dealt with more than one subject of taxation: National Trustees, Executors and Agency Co. of Australasia Ltd. v. Federal Commissioner of Taxation [1] .