Foucault, from The Order of Things:

Once similitude and signs are sundered from each other, two experiences can be established and two characters appear face to face. The madman, understood not as one who is sick but as an established and maintained deviant, as an indispensable cultural function, has become, in Western experience, the man of primitive resemblances. This character, as he is depicted in the novels or plays of the Baroque age, and as he was gradually institutionalized right up to the advent of nineteenth-century psychiatry, is the man who is alienated in analogy. He is the disordered player of the Same and the Other. He takes things for what they are not, and people one for another; he cuts his friends and recognizes complete strangers; he thinks he is unmasking when, in fact, he is putting on a mask. He inverts all values and all proportions, because he is constantly under the impression that he is deciphering signs: for him, the crown makes the king. In the cultural perception of the madman that prevailed up to the end of the eighteenth century, he is Different only in so far as he is unaware of Difference; he sees nothing but resemblances and signs of resemblance everywhere; for him all signs resemble one another, and all resemblances have the value of signs. At the other end of the cultural area, but brought close by symmetry, the poet is he who, beneath the named, constantly expected differences, rediscovers the buried kinships between things, their scattered resemblances. Beneath the established signs, and in spite of them, he hears another, deeper, discourse, which recalls the time when words glittered in the universal resemblance of things; in the language of the poet, the Sovereignty of the Same, so difficult to express, eclipses, the distinction existing between signs.