I will examine two key aspects of Evgeny Preobrazhensky's concept of 'primitive socialist accumulation': the notions that (a) the essential differences between socialism and capitalism are nationalised property and economic planning, and that (b) a transition from capitalism to socialism can take place through the extension of nationalised property and economic planning. Drawing on the work of Karl Marx and Raya Dunayevskaya, I will argue, first, that state property and economic planning are not the essential differences, and second, that Preobrazhensky's conception is one example of the view that political and legal changes are the determining factors in social change. That view, I will contend, inverts Marx's conception according to which political and legal relations correspond to and are determined by the mode of production, not vice-versa. If this latter view is accepted, I will further argue, the idea of a transitional society between capitalism and socialism is incoherent. This does not mean that social transformation must be instantaneous; what it means is that socialism cannot exist, partly or wholly, until the mode of production is revolutionised and that this cannot take place by political and/or legal means.