The laws of nature have an internal explanatory structure. This leads to interesting questions for metaphysicians of laws. What is the nature of this explanation? Marc Lange has recently argued in favor of metalaws: higher-order laws governing other laws, of which symmetry principles may be an example. Lange argues that his view, unlike its competitors, can make sense of the explanatory power of symmetries. I agree with Lange about the explanatory structure of laws but disagree with him about the nature of this explanation. I then present a Humean view that neatly captures the explanatory power of symmetry principles.

The universality of critical phenomena is best explained by appeal to the Renormalization Group (RG). Batterman and Morrison, among others, have claimed that this explanation is irreducible. I argue that the RG account is reducible but that the higher-level explanation ought not to be eliminated. I demonstrate that the key assumption on which the explanation relies—the scale invariance of critical systems—can be explained in lower-level terms. However, we should not replace the RG explanation with a bottom-up account; rather, we should acknowledge that the explanation appeals to dependencies that may be traced down to lower levels.

Quantum physics is the foundation for chemistry, but the concept of chemical bonding is not easily reconciled with quantum mechanical models of molecular systems. The quantum theory of atoms in molecules, developed by Richard F. W. Bader and colleagues, seeks to define bonding using a topological analysis of the electron density distribution. The “bond paths” identified by the analysis are posited as indicators of a special pair-wise physical relationship between atoms. While elements of the theory remain subject to debate, I argue that the quantum theory of atoms in molecules embodies a distinctive interactive conception of bonding that is an attractive alternative to others previously discussed.

Dmitrii Mendeleev’s periodic system is known for its predictive accuracy, but talk of its completeness is rarer. This is surprising because completeness (polnost’) was a quality that Mendeleev saw as important for a systematization of the chemical elements. Here, I explain how Mendeleev’s valuing of completeness influenced the development of his periodic system. After introducing five indicators of its completeness, I zoom into one in particular: Mendeleev’s inclusion of a schematic row of oxides. I then show how it guided Mendeleev’s predictions of indium and ekaboron, which suggests that the valuing of completeness was instrumental for making predictions.