According to Descartes, final causes have no place in physical theory, for in addition to being useless to seek them, teleological explanations can be a hindrance to scientific inquiry. For Leibniz, the demonstration by Fermat of the laws of reflection and refraction from the principle of minimum time is an indicative of order and finality in nature. The metaphysical postulate of a variational principle intrinsic to nature then becomes the correlate to the final cause, whose use facilitates the discovery of physical laws. The emergence, from Leibniz’s works, of an analytical mechanics based on the principle of minimal action raises new controversies regarding its teleological character. For even in the context of a deistic worldview, it would be left to show that divine wisdom would be compatible only with the simplicity of action and its minimal expenditure. Moreover, although in contemporary physics, both quantum and relativistic, there is a consensus about the validity and usefulness of the use of the variational principle in demonstrating the phenomena of nature and in obtaining its laws, its status – whether teleological or simply heuristic – remains an unresolved question. Some admit that nature possesses an immanent tendency to simplicity, others that “simplicity” only means that in the description of nature we must avoid complications.