An explanation of natural phenomena means knowing their causes. Since antiquity there have been philosophical debates about causes, the most famous of which is Aristotle’s theory of four causes. In modern science one of Aristotle’s causes — the active cause (causa efficiens) has been placed in the forefront, which has prevailed and modified the concept of force in modern philosophy of nature and science and has become one of the most important concepts of natural science. This concept remained unclear for a long time and was somewhat anthropomorphic and difficult to eliminate from science. Its formalisation and mathematical expression by I. Newton began a new scientific paradigm — the so-called classical mechanics that dominated science until the late 19th century. Newton «axiomatised« classical mechanics by setting law of forces acting in nature. His law of gravity became a universal law that applies to both celestial and terrestrial phenomena. Although Newton mentioned repulsive force, he said little about it. Only his followers asked about the theory of repulsive force, but all these discussions were secondary to the law of gravity. Ruđer Bošković, although a Newton follower, was the first to radically supplement Newton’s law of gravity by adding that there is a repulsive force between particles of matter at small distances. In this way, he created his concept of attractive--repulsive forces that does not represent two forces (as in the previous tradition) but rather is a single attractive-repulsive force which Bošković used to explain all phenomena in nature. This is the first case in science that all phenomena are explained by a single law. The paper discusses how Bošković overcame the dualism of force that was important for the establishment of some new concepts in modern science, which directly draw their roots from the Bošković’s theory of natural philosophy that was not any empirical theory but rather metaphysical one.