Michal Kalecki:

The innovation associated with methodologies close to Keynes like that of Michal Kalecki is to begin with the postulate that an oligopolistic market structure is an adequate characterisation of a modern economy. Therefore, the price of the product of an industry is the outcome of firms imposing a mark-up on average prime costs which are assumed to be approximately constant up to full capacity. The mark-up, synonymous with the degree of monopoly  of the industry, determines the profit margin and the share of profits in aggregate income. The level of profits is determined by the level of investment that entrepreneurs implement. In other words, pricing and investment behaviour determine the level of employment and output. The mark-up rate is believed to be relatively insensitive to the state of demand. Fluctuations in economic activity flow mainly from fluctuations in investment expenditures.