Articles 2(1) and 4(1) of the Sixth Council Directive 77/388/EEC must be interpreted as meaning that, in circumstances such as those of the case in the main proceedings — where a taxable person has acquired plots of land, some of which have been assigned to his private assets and others to his business and, where he has built, in his capacity as a taxable person, upon all of those plots of land, a shopping centre which was then sold together with the plots of land on which the building was erected — the sale of the plots of land which were assigned to that taxable person's private assets must be subject to value added tax since that person, at the time of that transaction, acted as such.