Following marx, it is appropriate to start, in setting out a coherent theoretical framework, with what marx considered as ‘the most fundamental law’ of political economy, namely from the law of the tendency of the rate of profit to fall (TrpF), which reveals that ‘the real barrier of capitalist production is capital itself’ (marx 1967, iii: 250). defining the average rate of profit (r) as the ratio of the total surplus value extracted by capital (s) in relation to the total capital invested, either in constant capital (C, concerning machinery, infrastructure and raw materials) or variable capital (V, concerning the payment of wages), we end up with the following relation:

r = s /(C + V).