Accounting is basically the entire sequence of processes of depicting and recording the economic activities of a business enterprise, preparing the financial statements, and communicating them to users. Since the 1960s, however, there has been a tendency to emphasize only one phase of the sequence of processes that comprise accounting, namely the relationship between the financial statements and the user, and to regard the remaining processes as subsidiary to that end. In this paper I shall argue that the duality which governs the process of depiction of economic activities is a fundamental characteristic of accounting, and I shall address methodological issues concerning the basic equations, which represent duality concepts concretely. The basic equation has been formulated in various ways, but essentially we may discern two viewpointsrone, which admits of only one formulation, and a second, which hypothetically allows for multiple formulations whose explanatory power is validated through practice. I shall argue here, in the first place, that the former viewpoint is inadequate both for calculative objectives and in its methodology of theory construction, and go on to demonstrate the validity of the latter viewpoint. Secondly, I shall consider four theories, the capital equation, Walb theory, the balance sheet equation and the business capital equation(or trial balance equation), and discuss their explanatory power by reference to the construct of calculative objects. In conclusion, I shall argue that the business capital equation has the highest explanatory power.