 Such applications of Curie’s principle depend, of course, on our accepting its validity, and this is something that has been questioned in the literature, especially in relation to spontaneous symmetry breaking (see below, next section). Different proposals have been offered for justifying the principle. We have presented it here as an example of symmetry considerations based on Leibniz’s PSR, while Curie himself seems to have regarded it as a form of the causality principle. In current literature, it has become standard to understand the principle as following from the invariance properties of deterministic physical laws. According to this “received view”, as first formulated in Chalmers (1970) and then developed in more recent literature (Ismael 1997, Belot 2003, Earman 2002), Curie’s principle is expressed in terms of the relationship between the symmetries of earlier and later states of a system, and the laws connecting these states. In fact, this is a misrepresentation of Curie’s original principle: Curie’s focus was on the case of co-existing, functionally related features of a system’s state, rather than temporally ordered cause and effect pairs. For a discussion on such questions as to whether there is more that one “Curie’s principle” and, independently of how it is formulated, what are the aspects that make it so scientically fruitful, see Castellani and Ismael, 2016. As regards the status of the principle, Norton (2016) argues that it is a “truism”, on the grounds that whether the principle succeeds or fails depends on how one chooses to attach causal labels to the scientific description. For Roberts (2013), Curie’s principle fails when the symmetry is time reversal. Roberts (2016) claims that the truth of the principle is contingent on special physical facts, and attributes to its failure an important role in the detection of parity violation and CP violation (on this point, see also Roberts, 2015, and Ashtekar, 2015).