This paper sketches a theoretical conception of modularity by generalizing Herbert Simon's idea of near-decomposability, showing that it could constitute a framework for the unification of the notion of modularity in the history and philosophy of biology. To put the framework to test, first a main problematic area is highlighted--the evolution of modularity--focusing on a historical and rational reconstruction of two ways of viewing it that appeared in the second half of the 20th century: one, due to Herbert Simon, rooted in a generic Darwinian mindset, the other, by Stuart Kauffman, inspired by a systemic-oriented approach tending to demote the importance of natural selection. It is shown that, under the light of the general view of modularity proposed here, these two apparently incompatible views can be interpreted as fundamentally homologous. The paper then engages with some current prominent views on modularity in biology, in order to show that the proposed framework is largely compatible with them, and able to accommodate cases of emergent modularity. The facilitating role of modularity in mechanistic and functional explanations is also highlighted. As a conclusion, it seems the proposed sketch of a theoretical view of modularity, open to further improvement, already shows potentiality as a unifying framework for the notion of modularity in philosophy and history of biology, and possibly, other disciplines.