For nearly a decade, Evanston photographer Melissa Ann Pinney, 62, has taken candid pictures of people and things in a variety of settings. But it wasn’t until 2013 that she noticed a theme: pairs—represented by couples, strangers, and even inanimate objects. Pinney’s friend, author Ann Patchett, noticed it, too. So they put together the book Two (Harper Design, $30, April 14), a striking collection of Pinney’s photos with essays by a number of notable writers, including Susan Orlean, Barbara Kingsolver, and Elizabeth Gilbert. Pinney shares the stories behind these four images.