Baudelaire uses rhyme in strikingly different ways. ‘Spleen’ and ‘L’Invitation au voyage’ can illustrate contrasting ends of one kind of spectrum.

Spleen

Pluviôse, irrité contre la ville entière,
De son urne à grands flots verse un froid ténébreux
Aux pâles habitants du voisin cimetière
Et la mortalité sur les faubourgs brumeux.

Mon chat sur le carreau cherchant une litière
Agite sans repos son corps maigre et galeux;
L’âme d’un vieux poète erre dans la gouttière
Avec la triste voix d’un fantôme frileux.

Le bourdon se lamente, et la bûche enfumée
Accompagne en fausset la pendule enrhumée
Cependant qu’en un jeu plein de sales parfums,

Héritage fatal d’une vieille hydropique,
Le beau valet de coeur et la dame de pique
Causent sinistrement de leurs amours défunts.

My French certainly isn’t good enough to know how this poem would read to a native speaker. However, and however naïve my detailed impressions may seem, I find it a miracle of concentrated evocation, both in its images and the texture of its language.

On the level of imagery, what’s so impressive is the abruptness with which pictures are juxtaposed, grand sweeping conceptions and dreamlike or nightmarish fantasy merging with or jostled by mundane realities. The tight grip of rhyme and metre give a feeling of inevitability to its unfolding, and what reason calls its fantastic elements seem as solidly present in the mindscape of the poem as its literal details, exercising as inescapable a force on the poet’s mood. Rhyme and metre also work to fold elements together – most mordantly in the sequence cimetière, litière, gouttière – cemetery, cat’s bed and gutter. This kind of folding together by sound seems to work within the lines as well as at their endings, for example in the ironic jarring of ‘carreau’ and ‘repos’, or the way the last syllable of ‘dans la gouttière’ twists the knife of ‘erre’. Power comes from the way ideas that are brought together in this way conflict with each other or cruelly intensify each other in meaning, sometimes both at once, as ‘cimetière’ and ‘litière’ do. This effect depends on the intensity with which the ideas are realised in themselves as well as the way they’re brought into relation with each other. The lines about the cat seem to me to me particularly evocative, brilliantly weaving the sense of the cat’s tense, restless movements and edgy state into their own phonetic texture. But these strongly, independently realised moments are yoked together in a kind of highly frictional harmony by sense as well as sound – not only by all presenting a mood of gloom tinged with horror but by imaginative parallels of other kinds, like the way the spectral poet’s voice, the lamenting of the bourdon – here, apparently, a bell ringing for the dead, not a bumble bee – the falsetto squeal of the smoky log and the wheezing of the clock gather in a cacophonous choir of voices that suddenly drop to the sad, sinister whispering of the Knave of Hearts and the Queen of Spades.

This kind of rhyming is quite opposite to what we find in ‘L’Invitation au voyage’:

Mon enfant, ma soeur,
Songe à la douceur
D’aller là-bas vivre ensemble!
Aimer à loisir,
Aimer et mourir
Au pays qui te ressemble!
Les soleils mouillés
De ces ciels brouillés
Pour mon esprit ont les charmes
Si mystérieux
De tes traîtres yeux,
Brillant à travers leurs larmes.

Là, tout n’est qu’ordre et beauté,
Luxe, calme et volupté.

Des meubles luisants,
Polis par les ans,
Décoreraient notre chambre;
Les plus rares fleurs
Mêlant leurs odeurs
Aux vagues senteurs de l’ambre,
Les riches plafonds,
Les miroirs profonds,
La splendeur orientale,
Tout y parlerait
À l’âme en secret
Sa douce langue natale.

Là, tout n’est qu’ordre et beauté,
Luxe, calme et volupté.

Vois sur ces canaux
Dormir ces vaisseaux
Dont l’humeur est vagabonde;
C’est pour assouvir
Ton moindre désir
Qu’ils viennent du bout du monde.
— Les soleils couchants
Revêtent les champs,
Les canaux, la ville entière,
D’hyacinthe et d’or;
Le monde s’endort
Dans une chaude lumière.

Là, tout n’est qu’ordre et beauté,
Luxe, calme et volupté.

In ‘Spleen’ images and ideas seem to struggle against the embrace of form, insisting on their gritty, individual reality, wrestling to break free of the poem’s dominion. In ‘L’Invitation au voyage’, the flow of sound and rhythm almost overwhelms visual and kinetic response. The effect is lovely and gently haunting, but to my mind far less powerful and less satisfying than ‘Spleen’, which I keep going back to. Every time I do it impresses me in new ways because it seems to give free play to so many divergent forces.