All About Love, By Lisa AppignanesiLove: a History, By Simon May

Our shelves groan with love. Out in the visual world, sex sells, but take down any novel, book of poetry or biography and it's clear that, on the page, love is most often the hook. As a magic word that all can use, but few define, its potency might be down to nothing more than the bewildering variety of experiences it covers, next to which the supposedly exotic range of options on the sexual menu seems staid. That this one word can be applied to romantic love, parental love, love between friends and love of God seems perverse, as if it is a deliberate semantic ploy to complicate and intensify our lives.

Love is present in all books, then, but all love present in one book? The idea seems absurd – surely it would expand until it reached the monstrous proportions of Robert Burton's The Anatomy of Melancholy. And, although Lisa Appignanesi does give Burton a nod with her book's subtitle, "Anatomy of an Unruly Emotion", she is more discursive, less relentlessly referential than him. Appignanesi approaches her subject through a simplified life-cycle, starting with young love, then long-term/married love, love in triangles, love in families (mother-love and infant-love) and finally friendship-love. Within each section she takes a historical run-up before attempting a general assessment of love's current status, with evidence gleaned from literature, psychology and the wider culture, as well as reflections on her own experience and brief accounts of anonymised interviews.

It's those historical run-ups that give the book its flavour. It is as if Appignanesi is holding up her pencil and squinting down the ages, so as to get the poets and philosophers of the past correctly in perspective, even as their thoughts about love rub shoulders with lesser, more recent contributions. So Proust looms large, with his narrator's memory of waiting for his goodnight kiss from Mamma, and Montaigne and Freud, but here too is Erica Jong's "zipless fuck", still just visible behind Bridget Jones, The Rules and even Mad Men, whose Don Draper tells a client that "romantic love was invented by people like me."

This is probably more of a panorama than an anatomy, but if it is an anatomy then it is one of an organism that hasn't finished evolving. The passages about attitudes among today's youth – on the one hand, far more blasé about sex than Jong ever was; on the other, brandishing ideals of continence and fidelity in reaction to their parents' permissiveness – read at times like an extended newspaper column, and presumably will read even more so in five or ten years' time. Which is to say that this is a book best read fresh, while Appignanesi's particular perspective matches what we see when we look out of our window.

All About Love is judicious and compendious, but you might argue that it is a little too much "about" love, in that it is often most engaging when its focus bleeds from the emotion itself into the adjacent topics of, say, child development or social history. Philosopher Simon May, by contrast, has written a book that sticks rigorously to its terms, that aims to give an account of love as a pure feeling, unencumbered by the effects and complications that arise when it is let loose on the world.

He, too, is after a historical explanation for "love" as understood today in the West. He interrogates various traditions and thinkers for the bits of their theories that we have, usually unconsciously, incorporated into our own. He starts with the injunctions to love God and your neighbour in Hebrew scripture, the exaltation of love as the route to the supreme values of beauty and goodness in Plato, and the synthesis of these two approaches in Christianity. Then all it took was the gradual decline of religion, and the rise of Romanticism, for love to fill the vacuum where God once stood – although May is quick to point out how often atheists, including Schopenhauer and Proust, attach a quasi-religious sense of redemption to their secular love.

Running through the whole book is May's own definition of love, which he links to "ontological rootedness". Love is "the rapture we feel for people and things that inspire in us the hope of an indestructible grounding for our life". As such, he dismisses the idea that love can ever be unconditional. Rather, it can be as unconditional as you want, so long as that sole condition is met – that the loved one holds the promise of helping us feel at home in the world. Once that goes, love dies.

It's a fair stab, and May even sketches out an internal development for his "ontological rootedness" in terms of those tricky foreign words that always ended up being translated as "love". Thus love begins as Eros (desire for the ontologically rooting person), hopefully ascends to agape (blissful submission to them) and finally achieves philia (intimate, reciprocal identification with them). "For", "to" and "with" – the conjunctions themselves suggest a trajectory to which most of us would aspire. It even fits neatly with the coda to Appignanesi's book, in which she eulogises the "temperate zone" of post-passionate love that, thanks to our increasing life expectancy, we can all hope to experience.