The rate constants hz for the attack of carbenium ions on an alkene, determined by Mayr for nonpolymerizing systems, are ca. 4 orders of magnitude greater than the k(p)(+) for the propagation of cationic polymerizations, which involve ostensibly the same reaction. This discrepancy is explained here as due to the different monomer concentrations [M] used in the two types of experiment. The argument starts from the fact that the planar, trigonal carbenium ion has two principal complexing sites, one on each side of the ion. These positions are competed for by all the constituents of the reaction mixture, which include the monomer, and therefore the characteristics of the ion are determined by the nature of its solvators. At high [M], the carbenium ions are predominantly solvated by the monomer, and they are less reactive than those complexed by the polar, but bulky solvent when [M] is low. The reason is that solvation by the pi -donor monomer on both sides reduces the charge density at the carbenium ion so much that the covalent bond formation to monomer, the propagation, requires a considerable activation energy. However, solvation by the solvent has a so much smaller effect on the charge density at the C+ atom, that the cation solvated only by solvent can polarize the incoming monomer sufficiently for the mutual potential energy between ion and molecule to lead to bond formation with little activation energy. Therefore, since the [M] in Mayr's experiments are smaller than those in the polymerizations, the cations in the two types of experiments are essentially different species, and therefore their kinetic constants are different. Mayr's rate constants are essentially the propagation rate constants extrapolated to [M] = 0, and they are likely to be all very similar for the same classes of monomers. The long quest for the "real" k(p)(+) has therefore been ended and the meaning of the k(p)(+) values selected by the present author has been established.