Descartes pines for the ultimate fresh start to human reasoning:
Thus also, those ancient cities which, from being at first only villages, have become, in course of time, large towns, are usually but ill laid out compared with the regularity constructed towns which a professional architect has freely planned on an open plain; so that although the several buildings of the former may often equal or surpass in beauty those of the latter, yet when one observes their indiscriminate juxtaposition, there a large one and here a small, and the consequent crookedness and irregularity of the streets, one is disposed to allege that chance rather than any human will guided by reason must have led to such an arrangement. . . . ~ Descartes, Discourse, Pt. 2
The ancient city grows organically—as it were—prompted by human need, the contingencies and exigencies of human life, the rise and fall of the glory of the city and the fortunes and misfortunes it encounters, and comes to possess its own soul, and its citizen is possessed by it:
The history of his city becomes for him the history of his own self. He understands the walls, the turreted gate, the dictate of the city council, and the folk festival like an illustrated diary of his youth, and he rediscovers for himself in all this his force, his purpose, his passion, his opinion, his foolishness, and his bad habits. He says to himself, here one could live, for here one can live, and here one will be able to go on living, because we are tenacious and do not collapse overnight. Thus, with this “We” he looks back over the amazing past lives of individuals and feels himself as the spirit of the house, the family, and the city. From time to time he personally greets from the distant, obscure, and confused centuries the soul of his people as his own soul. ~ Nietzsche, ADHL, §3.
This image of a human tradition rooted in natural human need and teleology captured in the image of a city, that great completion of the political element of human nature, Descartes turns to his own devices. For the old manner of city seems apart from “any human will guided by reason,” and thus Descartes initiates the modern turn by turning human nature and setting it in opposition to human reason. In the same way, he says, are we to think about the human tradition of inquiry to complete the speculative element of our nature:
In the same way I thought that the sciences contained in books (such of them at least as are made up of probable reasonings, without demonstrations), composed as they are of the opinions of many different individuals massed together, are farther removed from truth than the simple inferences which a man of good sense using his natural and unprejudiced judgment draws respecting the matters of his experience. And because we have all to pass through a state of infancy to manhood, and have been of necessity, for a length of time, governed by our desires and preceptors (whose dictates were frequently conflicting, while neither perhaps always counselled us for the best), I farther concluded that it is almost impossible that our judgments can be so correct or solid as they would have been, had our reason been mature from the moment of our birth, and had we always been guided by it alone. ~ Descartes, ibid.
Descartes wishes for an unreal city. Against the second nature of custom he hopes to introspectively recover a counterfactually pure and always “mature” reason, as if to hold it apart from possibly erroneous external influences “from the moment of our birth.” This is a rationalism that strains unnaturally against the innate character of the human mind, naturally situated for inquiry within the cosmos, just as we are naturally ordered to a complete life in the civil order.