Susie Boyt is gripped by two novels about passion and procreation: Venus Flaring by Suzannah Dunn, Flamingo, pounds 9.99 x Common Ground by Andrew Cowan, Michael Joseph, pounds 13.99
When I was at university, Jacques Derrida came and gave a talk about his ideas. When asked about the direction of his current work, he said he had been thinking about friendship. When two friends meet, he told us, the one thing they know for certain is that one of them must die before the other.

I thought of this while reading Suzannah Dunn's fourth novel, Venus Flaring, because the book charts the life and death of a friendship of such intensity and ardour that both the girls involved and the reader know that this degree of feeling cannot be sustained forever. What we feel is not that one friend will die first, but that one girl will cool towards the other, and to the one that is left this will seem like a death.

Ornella Marini is passionate, outspoken and mercurial, and her friendship for the quirky but sensible Veronica, the narrator, begins on the hockey pitch, when the two girls are so dismayed by the cold that it helps them develop a sort of Dunkirk spirit. As their friendship blossoms like a romance, Ornella is always at its centre, always the star. She has a glamour to her, engineering trips to Wimpy bars and being spectacularly cheeky to the teachers. In an English class, when told that Jane Austen is presenting Frank Churchill as a dandy who goes to London for a haircut, Ornella won't accept this. "He's a junkie," she says. "He's going to London to replenish his supply."

Ornella also demands a lot of care. When she takes an overdose after her boyfriend leaves her, Veronica goes to her house every evening and returns home to the prospect of long phone calls stretching into the night - and yet Veronica relishes the closeness. Dunn presents a friendship that is obsessive, whilst making it quite clear that this is what friendships between adolescent girls are often like, when teenagers are working out whether it is possible to be everything to another person.

The chapters that herald the decline of the friendship are painful to read. The loss of Ornella seems intolerable to Veronica, and yet it becomes clear that their intimacy was sustained by moments of crisis, and as they grow up and settle into patterns of love and work, the crises diminish and there is little left to bind them to each other. I'm not quite sure that the history of this friendship is enough to sustain a whole book. I would have liked to have known more about the girls' families and what it was about them that caused this kind of dependency. However, this is a sensitive and often funny story, that impressively treats a friendship between young women with the sort of grandness and ceremony usually reserved (by novelists) for love affairs.

One of the most striking and admirable aspects of Andrew Cowan's writing is his ability to evoke subtle nuances of mood and atmosphere using an absolute minimum of words and hardly any adjectives at all. In his first novel, Pig, this withdrawn and poignant style exactly suited his subject matter, the sharp and unsafe world of adolescence, and the effect was a brave and quiet sort of magic. Common Ground, Cowan's second novel, has the same kind of integrity: a fidelity to ordinary words and ordinary occurrences, strong characters and a powerful feel for urban decay. And yet this book seems to lack something of the wonder of the earlier novel: at times it can seem too inward-looking, too bleak, as it charts 18 months in the life of a young couple - Ashley (a disaffected Geography teacher) and Jay (a printer in a community arts project) - and takes them from the first months of Jay's pregnancy to the birth of their daughter Maggie, and beyond.

The landscape of this novel is extremely grim. The view from Jay and Ashley's house can take in a man peeing into the front seats of a car through the window he has just smashed, or a young boy having the living daylights kicked out of him by a gang of youths. Used syringes pile up. Ashley's delight at seeing an adolescent dancing in the street with his mother is shattered as the son sticks his tongue in his mother's mouth and she swears at him.

The question that Common Ground seems to have at its heart is: what can you do for hope in an environment like this? The answers come from several directions. You can love someone and bring a child into this world. You can take a different stake in the future, as Jay does when she becomes involved in a campaign against a new motorway, or, like Ashley's brother Douglas, you can throw in the towel and go travelling.

The brothers correspond with each other, sometimes humorously, sometimes crassly, as Douglas makes his way through Asia, allowing Ashley an outlet for his anxieties, disappointments and delight about the baby as Jay becomes increasingly consumed by the demonstration against the motorway. The minor characters are convincing, and importantly emphasise the way that having a baby can force one to review one's own experience of family life.

Jay's grey-plaited, hippy mother comes and goes in her bus, in a world of her own,contributing peaceful maxims, whilst Ashley's mother drops in for long cleaning sessions and acidic criticisms of his father, who sits in the car and is brought cups of tea by his son. This is a fine and acutely perceived novel. The final image of the new little family unit fleeing destruction is terrifying, but perhaps offers a thin promise of release.