Coherently with his negative judgement on civilisation (that by destroying illusions makes man unhappy), Leopardi in his theoretical reflections depreciates reason and instead exalts imagination, passion, nature:

 

“it is the enemy of nature; and nature is great, and reason is small” [14-5, 116, 270-1, 341-2, 375, 403-5] – the progress of reason has provoked the loss of great men, and by destroying illusions it has fomented egoism [21-3, 160-1]; hence despotism [160-1] – it makes us neither happy nor wise [103] – together with philosophy, it has made life arid [111] – the civilisation of a nation is born of a blending of nature and (in lesser measure) reason [114-5] – it is never as effective as passion [293-4, 3237-45] – “it is so barbarous that wherever it occupies first place ... everything becomes barbarous” [356] – the cult of the goddess of Reason during the French Revolution [357] – “The perfection of reason is absolutely not the perfection of man, but rather of man as he is after corruption” [405] – it is perfect if it allows one to know one’s insufficiency [407, 1163, 1337] – relationship between reason and Christianity [427, 1065] – the inferiority of reason with respect to nature, verification in the consideration of governments [543-79] – “The man the most certain of the militia of men, reconciles himself with mankind ... if even momentarily does he receive some good treatment ... This is the grand strength of reason in man!” [1727-8] – reason “needs the imagination and illusions it destroys” [1839] – it is harmful, because it takes away the importance of things to the point that it reduces them to nothing [2941-3] – it is inferior to nature also in poetry, as demonstrated by the comparison between Homer and the epic poets that followed [3615] – as is nature, so is reason contrary to society that straitjackets [3930] – “simple reason, virgin and uneducated, very often judges more correctly than wisdom, that is cultivated and indoctrinated reason” [4477-8].