Significance: Electrophilic substitution is universally regarded as the characteristic reaction of aromatic compounds. Arenium ions are widely accepted as obligatory intermediates in the two-stage (S _E Ar) mechanism typically described in textbooks, monographs, and reviews. We now challenge this mechanistic paradigm. Our combined computational and experimental investigation of the exemplary halogenation of anisole with Cl ₂ in CCl ₄ finds that addition–elimination pathways compete with the direct substitution process and also account for the ortho – para orientation preferences easily. Moreover, the S _E Ar processes do not involve arenium ion pair intermediates , but proceed instead via concerted one-stage single transition state routes. We question not only the generality of the accepted S _E Ar mechanism, but also the involvement of arenium ion intermediates, when counter ions are present.