Acceleration of a chemical transformation by a species that accepts a proton or donates an electron pair to a substrate defines base catalysis. In general base catalysis a proton is partially transferred in the rate-determining step and the catalyst is regenerated; in specific base catalysis the active nucleophile is the lyate ion formed in a prior equilibrium. Lewis base catalysis is the complementary closed-shell process in which the catalyst binds a Lewis-acidic site (a carbonyl carbon, a silicon center, or a π-acidic metal) and thereby activates the substrate without net proton transfer ^[1]. Dual catalytic systems may combine a Lewis base with a photoredox cycle so that the two catalysts jointly generate the nucleophilic and electrophilic partners of a C–C bond-forming step ^[2]. In ribonucleic acid catalysis, general acid–base catalysis likewise proceeds by concerted proton transfer at the phosphodiester, underscoring that the defining elementary act is proton shuttling rather than metal redox chemistry ^[3]. The concept excludes stoichiometric use of a strong base as a reagent: the base must be turned over. It is complementary to acid catalysis, which activates by proton donation or Lewis-acid coordination ^[1].