Given the proverbial French appetites and aptitudes, it's perhaps not surprising that Martin Turnell finds love to be a preoccupation that has shaped the style and substance of the French novel from the beginning. That beginning came in the 18th century, when prose fiction searched for a respectable audience by developing techniques capable of convincing readers that what they read was not vulgar invention but arresting truth--hence the novel as letters, or as memoir, or autobiography. These technical devices gave rise to a literature of private lives lived on the fringes of accepted morality--i.e., a literature of ""love and social criticism."" Turnell follows this desire to convince in its fictional manifestations through selected works of seven authors (a different group than he dealt with in previous books on French fiction). Marivaux dwells on the equivocal morality that reproves illicit love but rewards its practitioners with social acceptance. Crebillon fils portrays a society grown callous which transfers sex from the realm of love to that of taste and then to that of commerce where it falls under the shadow of cruelty. Rousseau seeks to rejoin sex with love and sensibility, thereby to improve and expand the emotional life. Stendhal and Flaubert, enjoying a language much richer than the 18th century knew, depict emotional selves contending with a complex and unstable material world--which prompts Turnell to a lengthy and suggestive comparison of Flaubert's prose style with cinema. Finally, Alain-Fournier and Raymond Radiquet disclose for the first time the secrets of adolescent love. Although Turnell's range is wide and his subject promising, the book relies over-much on detailed plot summaries and off-hand explications, and reaches the lame conclusion that ""all lovers whatever the period and the conditions of society in which they live"" betray ""fundamental resemblances between heart and mind."" Of academic interest chiefly.