Of such a process, the whole of Croce's philosophy is a continuous exemplification, but nowhere so clearly apparent as in the progress of his conception of history. His first step had been that of reducing history to the general concept of art, thereby emphasizing the concreteness and individuality of history, as opposed to the abstractness of the natural sciences, the concepts of which, in that early stage, he could not yet distinguish from those of philosophy. In the _Estetica_ the conception is still practically the same, history resulting from the intersection of art and philosophy through the application of the predicate of existence to the intuitive material. In his first _Lineamenti di Logica_, history appears as the ultimate product of the theoretical spirit, "the sea to which the river of art flowed, swollen by the waters of the river of philosophy." But in the same _Lineamenti_ he had not yet arrived at the identification of the definition and the individual judgment, which in his second _Logica_ constitutes the final form of the pure concept, Croce's original interpretation of Kant's _a priori_ synthesis. Between the first and the second _Logica_, Croce wrote his _Filosofia della pratica_, in which he denied the duality of intention and action, as in the _Estetica_ he had denied the duality of intuition and expression: an intention which was not also an action appeared to him, as we shall see, inconceivable. It was by analogy with his treatment of this duality, that he solved the duality between the concept (in the sense of definition) and the individual judgment, which was also a duality of philosophy as antecedent and history as consequent, as he perceived that a concept which is not at the same time a judgment of the particular is as unreal as an intention which is not at the same time an action.