Poetry is distinguished from prose by constraints on form (that of verse), but also by constraints on syntax and lexicon (that of “delicate taste”, which obliges us to replace mariage by hymen and ventre by sein - see Ténint 1844). The influence of the classics maintained the value of this double set of constraints well into the nineteenth century. So, when “prosaic verse” (a syntactically ternary alexandrine) took off in France with Romantic poetry, it was devalued as “rhymed prose”. Writers nevertheless demanded greater freedom for poetry. In his preface to Cromwell, Hugo called for verse that “dares to say everything” and is “as beautiful as prose”. This was also the path taken by Baudelaire in Les Fleurs du mal, with all the legal setbacks that went with it. Prosaism thus presented a risk, even a threat, to the ideal of poetry.With Petits poèmes en prose, the same Baudelaire undertook a more radical project. A new game is played here, in which considerations of both form and lexicon come into play. On the one hand, the prose form found a musicality that distanced it from “flowing prose” (draft preface to Les Fleurs du mal); on the other, the lexicon took in all the details of reality. In this way, semantic prosaism is combined with a kind of formal “poeticism” (Dessons 2002). The study of the poem “Les projets” will demonstrate this.