The salient feature of Croce's mind, fully displaying itself in the maturity of his work, is a power to follow different lines of thought and research, without either confusing the issues or losing sight of the deep underlying connections. For the average scholar, an incursion into alien ground will generally mark the abandonment of his former interests; or, in the best hypothesis, the creation of a new mental personality coexisting with the original one, but neither reacting on it nor being influenced by it. The reason is obvious: the substance of each personality is a cross-section of the body of one discipline, which in its actual history, in its methods, associations and sphere of interest, touches the other one at very few points only, if at any at all. The establishment of new relations between the two requires a new personal elaboration, a complete individual mastery of the materials and methods of each discipline. We are hardly aware of the independence gained by even very closely related fields of research through the specialists treatment of the last century: how each of them has developed, so to speak, a language of its own, which has its foundation in the peculiar, and inevitable, terminology, but extends far beyond it into the logical structure of the specialist mind. We have more or less consciously built up a world (that is, an implicit conception of the world, a naïve philosophy) for the economist, one for the biologist, one for the mathematician, one for the student of literature, and so on. The scholar with the dual personality lives alternatively in separate and self-contained worlds; but to melt the two images into a single one, is far beyond his power. In other cases, he will relate all the experiences legitimately belonging to one special world, to another one, probably to the one with which he was first acquainted; but then we have those awkward hybrids, the economics of the literary man, or the literature of the biologist, or the biology of the economist; and the confusion is so apparent that it generally reflects itself in the very quality of the terminology employed.