Contributor(s): AS Byatt, Ben Okri, Helen Simpson, Colin Thubron | Four very different writers consider four very different aspects of love: love as enchantment, and love as madness; passion in youth, and compassion in age. They read their favourite passages on love both from their own work, and from the work of others, and, on Valentine's eve, discuss Shakespeare's notion that 'The lunatic, the lover and the poet are of imagination all compact'.