Verlaine’s reputation is not as high as it once was, and this is largely because his poetry lacks the depth of that of his greatest contemporaries. Poets such as Charles Baudelaire and Stéphane Mallarmé were nearly as technically proficient as Verlaine, but they had thought deeply about life and the relation of poetry to life in a way that Verlaine had not. Rimbaud, contrastingly, was less technically skilled than Verlaine, but Rimbaud’s lack of emphasis on poetic form followed from a principled and logically consistent rejection of much of tradition, also indicative of serious thought.

Yet there was a disarming feature of Verlaine. He both acknowledged his shallowness and defended himself by arguing that a kind of mistiness in thought was necessary to convey the type of limpidity for which he strove in his writing. In “L’Art poétique,” published in the volume Jadis et naguère (1884), he wrote, “De la musique avant toute chose” (“Music before all things”), and stated that it is best to accomplish that by creating verse “où l’Indécis au Précis se joint” (“where the undefined and precise join”). In other words, to capture an ineffable mood it is necessary to have an underlying structure of thought that is itself rather vague and incomplete. It is hard to argue with his advice, especially since his work is preeminent in French literature in being able to convey delicate, illusive feelings.

It is important to be aware of how he speaks of a combination of the precise and imprecise, for it is not merely by the use of vague words that he creates his moods—his effects cannot be achieved so easily. He combines vagueness and concreteness in precisely the right measure. In “Il faut, voyez-vous, nous pardonner les choses” (“You see, we have to learn to pardon all”), his method of combination can be seen. (This poem, like many of his poems, takes its title from its first line.) The speaker is asking for forgiveness, and he wishes that he and the listener could return to their childish innocence. Exactly what is to be forgiven is left tremulously vague; yet, at the right moment, a concrete image is introduced, a description of frightened little girls who feel enormously guilty for a minor lapse. This image gives the speaker’s suit a poignance based in reality, though still a reality only analogically related to his continuingly unclear original sins.

Three other traits help Verlaine in his quest for distinct indistinctness: musicality, conversational tone, and natural imagery. The verbal music, which he put before all things, was that of an easy lilt and a graceful chiming of vowels and consonants that gave his verse a prettiness that few other poets have matched. In poems such as “Chanson d’automne” (“Song of Autumn”) and “Il pleure dans mon coeur” (“It Is Crying in My Heart”), the easy grace of the lines creates a melody that connects sympathetically to the tremulous passages of a weary sadness.

At the same time, adding to the poetry’s weight and thus balancing its tendency toward evanescence, is a conversational tone that conceals the artistry of the work by creating the sense of listening to a relaxed monologue. Thus, Verlaine may open a poem with an unaffected statement such as “Tournez, tournez, bons chevaux de bois” (“Turn, turn wooden horses”—carousel horses), or with a casual request, as in “Écoutez la chanson bien douce” (“Listen to the sweet song”). In order to embody this tone, Verlaine made a number of innovations and reemphases in the rather strict conventions of French verse. For one, against the more strident practices of Romanticism, he preferred weak rhymes, ones that called less attention to themselves. He broke with the tradition of having a caesura, a brief pause of sense and sound at the middle of the typical twelve-syllable line. Moreover, he worked less with the preferred twelve-count line than with shorter measures and particularly, unusually, ones of odd-numbered syllables, from five to thirteen. He also practiced enjambment (rejet in French), that is, the method of not ending a clause and sense unit at the line’s end but carrying it over to the following line. None of these alterations in standard procedures was made as a technical experiment, but each was done to deemphasize the rigidity and formality of verse (factors that proclaimed, “this is a poem”) in favor of naturalness.

This naturalness, too, helped create the necessary vagueness, which would have been harder to reach within the tougher shell of stricter methods. Verlaine also conveyed this prized quality by choosing to portray nature in its filmy moods. He begins his celebrated “En sourdine” (“Muted”) by describing a wooded glade, “Calmes dans le demi-jour/ Que les branches hautes font” (“Calmly in the twilight/ Created by the upper boughs”). “L’Heure du berger” (“Dusk”) begins “La lune est rouge au brumeux horizon;/ Dans un brouillard qui danse” (“The moon is red along the smoking horizon;/ In a shifting mist”). In each case, a shuttered half-light and the incompletely discerned shapes of foliage or of the sun draw the reader into a web of a twilight world in which formless emotions appear.

More specifically, what were the emotions of which the poet sang? It might be said that Verlaine’s feelings are not those of the will, such as hatred and passionate desire, but those of passivity, such as nostalgia, regret, and unrequited longing. Thus, in “Mon rêve...