"First and last what is required of genius is love of truth." (Goethe, Maxims and Reflections) 

Although art's forms are designed and are guided by precept and example, they must not appear to be designed: there must be no trace of a rule impeding or inhibiting the artist's mental powers. For Kant, the capacity or talent to produce such forms is "genius." " Genius is the mental disposition (ingenium ) through which nature gives rule to art." (Critique of Judgement, p. 150) 

Kant's aesthetic is based on a distinction between reason's requirements for determinate concepts, and the indeterminate, yet universal quality of aesthetic judgement. For Kant, natural beauty is the prime paradigm, because it is not a product guided by concept (a design). Yet when we judge nature aesthetically, we impute the "mere" form of cognisibility to it. In Kant's terminology, the aesthetic judgement of nature requires that we think of nature as "purposive without purpose." 

Art, as opposed to nature, is always the product of a concept (of art, for example). Only the art of genius allows that concept to be indeterminate rather than determinate. The genius does not create through rules, but produces an indeterminate form through the harmonious play of the faculties. Although the rule is not a conscious concept guiding the genius in the creation of beautiful art, other talented individuals can intuit and abstract the rule from the products of genius. (see Gasché, pp 186 ff.) 

"Genius detects through the fly, through the caterpillar, through the grub, through the egg, the constant individual, through countless individuals the fixed species, through many species the genus; through all genera the steadfast type, through all kingdoms of organized life the eternal unity. Nature is a mutable cloud which is always and never the same." Emerson (Modern Anthology, p.31)

A more contemporary, or postmodern view of genius, practiced by Pierre Bourdieu, would see the "great painter" not as endowed with some inner richness, but in a almost military manner -- as someone who takes advantage of an objective possibility, based on a superiority of technique and terrain, assessment of the counterforces, and a shrewd maximization of one's own specific and idiosyncratic resources. (Jameson, p.306)