T. V. F. Brogan argues that "genius" is a middle term in the evolution of the idea of inspiration and poetic ability from a belief in an external source (afflatus, or divine infection, and poetic phrenzy, or divine madness) and an internal source (imagination and the subconscious).
At the same time, Romanticism's definition of genius as a person driven by a force beyond his or her control and as an ability that surpasses the natural and exceeds the human mind makes it virtually identical with the Classical notion of divine madness or frenzy.
With the incorporation of Sigmund Freud's theories of poetic madness and the irrationality of imagination deriving from the subconscious, "genius" in poetry entered 20th century critical parlance as, again, something inherent in the writer.
Such an image of genius is often defined in opposition to the figure of the critic, the former being more independent and spontaneous in their thought, the latter being more self-reflective but consequently restricted to responding to, rather than creating, enduring cultural artifacts.
The earliest version of this formulation is to be found in Gotthold Ephraim Lessing's commentary on Immanuel Kant's notion of genius.