The originality of the imaginative concepts, terms and symbols of the classical Spanish mystics has elicited several philological approaches. All of them try to explain or rather to account for this originality. Each of these different methods, however, is characterized by a striking onesidedness and exclusiveness of view. In order to find out where further research has to start from, it is necessary first to review the attempts of investigation made till now. They may be designated as the non-historic, the synthetic, the secular, the Arabic and the Germanic theses.