Initially, Lacan proposed that the mirror stage was part of an infant's development from 6 to 18 months, as outlined at the Fourteenth International Psychoanalytical Congress at Marienbad in 1936. By the early 1950s, Lacan's concept of the mirror stage had evolved: he no longer considered the mirror stage as a moment in the life of the infant, but as representing a permanent structure of subjectivity, or as the paradigm of "Imaginary order". This evolution in Lacan's thinking becomes clear in his later essay titled "The Subversion of the Subject and the Dialectic of Desire".