This paper represents an attempt to clarify the field of the studies concerning the poor stagnant economy. Using systemic analysis the original theories are reformulated in such a way as to highlight their similarities and dynamic structure. The works of Ragnar Nurkse, Gunnar Myrdal, John K. Galbraith and Harvey Leibenstein are presented as components of a general theory of stagnation at low incomes. The paper ends with an attempt to formulate a 'modern version' of the theory, using the 'chaotic dynamics approach' to depict the situation. The main purpose of this paper is to 'formulate' the concept or, in other words, to clarify mathematically the hypothesis in order to test it. The building of the empirical tests and of economic models to explain it is treated in other papers.