The originality of an era is not measured by the content of its ideological systems but rather by its “selective will,” that is, according to the interpretive grille it interposes between preexisting contents and their “modern” treatment. The passing of a message through the hermeneutic filter of an era produces two results of a semantic kind: the first, aiming at the very organization of the cultural structure of the time and hence located outside it, is set forth as a complex and subtle mechanism of emphasis or, on the contrary, of suppression of certain ideological contents; the second, which operates in the very interior of the cultural structure, is set forth as a systematic distortion or even a semantic inversion of ideas which pass through the interpretive grille of the era.
All of this means that the crowning wish of the historian of ideas is not, or should not be, to define the ideological contents of a given period, which are fundamentally recursive in nature, but to glimpse its hermeneutic filter, its “selective will,” which is, at the same time, a will to distort.
An ideology can be described; a system of interpretation – the only one that counts because it alone can show what the originality of one cultural moment in time relative to every other is capable of – is imperceptible. An implicit if not a hidden presence but also an objective and ineluctible one, it is revealed stealthily in all its complexity only to immediately escape the observation of the investigator. In order for him to practice the history of ideas, he is called upon to see not only what is preeminently revealed, the ideas themselves, but precisely that which is not revealed, the hidden threads that link ideas to the invisible will of the time, their producer. Ideas are seen by everyone; the historian of ideas is supposed to look in the wings, to contemplate another aspect of the theater, the stage seen from within.
– Eros and Magic in the Renaissance (1987), pp. 11-2