But one need only take a look at the account of a phenomenon based on the opposition of these forces (any will do; for instance, the uneven speed of a planet in its orbit around its central body) to become immediately aware of the confusion that reigns in it, and the impossibility of sorting out the quantity of the two forces, with the result that the one force which in the explanation is assumed to be decreasing must always be taken just as well as increasing, and vice versa.