profession or vocation; (v) income from other sources; and (vi) capital gains. The scheme of the Act is that income tax is one tax. Section 6 only classifies the taxable income under different heads for the purpose of computation of the net income of the assessee. Though for the purpose of computation of the income, interest on securities is separately classified, income by way of interest from securities does not cease to be part of the income from business if the securities are part of the trading assets. Whether a particular income is part of the income from a business falls to be decided not on the basis of the provisions of Section 6 but on commercial principles. To put it in other words, did the securities in the present case which yielded the income form part of the trading assets of the assessee? The Tribunal and the High Court found that they were the assessee's trading assets and the Civil Appeal No.3291­3294 of 2009, etc. Page 25 of 45income therefrom was, therefore, the