The explanation of the hypothetical HAlCl4 acid instability is provided on the basis of theoretical considerations supported by ab initio calculations. The equilibrium structures of LiAlCl4, NaAlCl4, and KAlCl4 salts were examined and compared to that of their corresponding parent acid. The process of formation of the representative NaAlCl4 salt was analyzed, and the interaction energy between NaCl and AlCl3 was estimated to be ca. 55 kcal/mol while that between HCl and AlCl3 (when the HAlCl4 species is formed) was calculated to be smaller by in order of magnitude (ca. 8 kcal/mol). The hypothetical HAlCl4 acid was identified as an HCl center dot center dot center dot AlCl3 adduct (with the hydrogen chloride tethered weakly to the quasi-planar aluminum chloride molecule). The electron affinity of the neutral AlCl4 superhalogen molecule was found to be the factor determining the ability to form a stable compound of MAlCl4 type.