There are many other examples concerning the validity of assumptions. For instance, in the photochemistry of electronically excited states, the Kasha rule dictates that excited states always emit from the lowest energy level of a given spin multiplicity, which assumes that the internal conversion is faster than emission. However, anti-Kasha emission happens when internal conversion occurs more rapidly than emission, usually as a result of large energy gaps between excited states. In a separate example, ligand field theory assumes that in organometallic complexes, ligands are more electronegative than metals and have frontier orbitals of lower energy than those of the d orbitals of electropositive metals. When moving to the right in the dblock and approaching the transition-metal/main group boundary, the d orbitals become more core-like, making their cations more electronegative, eventually arriving at a point where they are lower in energy than the ligand frontier orbitals, resulting in inverted ligand field theory. These examples should remind us to examine these two aspects of each scientific conclusion: 1) given that the assumptions are valid, whether the deduction is logically correct; and 2) whether the assumptions themselves are valid. Asking more "what if" questions are always beneficial in critically evaluating assumptions.