A third, only marginally related concept was proposed in 1923 by Gilbert N. Lewis, which includes reactions with acid–base characteristics that do not involve a proton transfer.
ɐ θˈɜːd, ˈoʊnli mˈɑːɹdʒɪnəli ɹᵻlˈeɪɾᵻd kˈɑːnsɛpt wʌz pɹəpˈoʊzd ɪn nˈaɪntiːnhˈʌndɹɪd twˈɛnti θɹˈiː baɪ ɡˈɪlbɚt ˈɛn. lˈuːɪs, wˌɪtʃ ɪŋklˈuːdz ɹɪˈækʃənz wɪð ˈæsɪd bˈeɪs kˌæɹɪktɚɹˈɪstɪks ðæt duːnˌɑːt ɪnvˈɑːlv ɐ pɹˈoʊtɑːn tɹˈænsfɜː.