The words "dandy" and "flaneur" are often used as terms of disparagement, the former for a man who pays too much attention to his clothes, the latter as a lounger with no sense of purpose. Baudelaire, however, uses these terms in a highly technical sense as part of his aesthetic philosophy. In "The Painter of Modern Life," he writes that the word "dandy" implies

a quintessence of character and a subtle understanding of all the moral mechanisms of this world; but, from another aspect, the dandy aspires to cold detachment.

He says that he has no hesitation in describing M. Guys as a dandy, since he has a dandy's aesthetic attitudes to the subjects he selects as a painter and the way in which he presents them.

M. Guys is a flaneur, according to Baudelaire, in his affinity for the great crowds which characterize modern life in Paris (and which often feature in Baudelaire's poetry). Baudelaire writes:

The crowd is his domain, just as the air is the bird’s, and water that of the fish. His passion and his profession is to merge with the crowd.

This is a source of pleasure for every idler, but Baudelaire goes on to assert that Guys has a nobler and more general aim than that of the flaneur who is not also a dandy and an artist when he immerses himself in the crowd:

He is looking for that indefinable something we may be allowed to call "modernity," for want of a better term to express the idea in question. The aim for him is to extract from fashion the poetry that resides in its historical envelope, to distill the eternal from the transitory.

In his selection and treatment of modern, dynamic subjects, therefore, the quintessential modern painter is both a dandy and a flaneur.