Our book today is Unconditional: Older Dogs, Deeper Love, a glorious result of photographer Jane Sobel Klonsky’s journeys around the United States, talking to people about their old dogs. This is a book that will bring a painful smile to the face of any dog owner, because its subject is the contradiction at the heart of the relationship.

Dogs are not stately, like horses, and they aren’t stealthy, like cats; they’re direct, bounding – active. We instinctively picture them running, jumping, (occasionally something that rhymes with ‘jumping’), playing; the dog is, as Henry Ward Beecher immortally put it, the god of frolic.

It’s a mental fixed point that makes their old age feel almost like some kind of contractual failure. Surely, the dog owner thinks every time, this old, stiff, staring duffer can’t be the same animal I held in my hand as a squirming little milk-puppy just a little while ago? The question is equal parts astonished and defensive; the easiest thing to forget, in their long sunshine years of bottomless vitality, is that dogs age ten times faster than their humans. The sheer speed with which their old age comes upon them shouldn’t be a surprise to anybody who’s seen how fast a puppy achieves adulthood, and yet it always is a surprise. Suddenly, virtually overnight, the same person who could once leap up into your outstretched arms from a standing start needs your careful, gentle help to get up on a mattress hardly taller than your hand. And the surprise moves in both directions: they’re not exactly a species known for their sharp introspection, but even so, old dogs know they’re lessened. There’s a quick look of fear that crosses their eyes when some jump fails or some new pain flares up – fear and uncertainty. On some level, they’re often aware that some fundamental term of the compact with their humans isn’t being met anymore.

That’s where the “unconditional” of Klonsky’s title comes in. The owners she interviews and photographs are doing everything they can, every day, to alleviate those little moment of fear and uncertainty. Whether it’s Todd Collins and his 17-year-old Cheyenne, or Stacy Cohen and her 10-year-old mastiff Josie, or Sheryl Maloney and her 12-year-old golden retriever Hannah (“People may think I am silly, but I love here like she is my child, my best friend, and my soul mate. I can’t imagine these last 12 years without her by my side”), the sentiments recorded in these pages hit the same notes over and over: “She’s a gift to me,” “He’s given me more than I could ever give him,” “I am forever indebted.”

It takes a great deal of patience to care for the elderly, and this is no different for dogs than it is for humans. That patience virtually glows off these pages. John Hembree, for example, has a 13-year-old pointer named Forrest who’s suffering from an incurable spinal degeneration called myelopathy, causing the dog slowly to go lame – and Hembree has fitted him out with a metal framework on wheels, determined to do whatever it takes to keep Forrest enjoying life. Likewise Jen DeVere and her 17-year-old spaniel mix Avery, who’s been through a host of health problems but still wants to enjoy every day. “The doctors have told us that she seems to be in good spirits, so we get to have her with us a little longer,” says DeVere. “Every day is gift with her. When she woofs and wags her tail in her sleep, it still makes me smile, and I know all the effort is worth it.”

That sentiment – that every day is a gift – is shared in some capacity by every single human interviewed in Unconditional. Certain Norma-Desmondesque basset hounds notwithstanding, most dogs in their prime lavish their human companions with love and energy, and when the end comes, the awful burden of returning that great gift shifts to its recipients, who will either rise to the example that’s been set for them or fail. Anybody who’s ever worked or volunteered at a dog pound will know the dead-eyed look on the faces of the humans who fail, but such horrible moments aren’t captured in books and never will be and shouldn’t be. It’s the other group that’s celebrated here: these are the dog owners who’ve learned selflessness from their old friends. And these are the faces of those old friends – no longer able to pester or guard or guide, needing all the help they once so eagerly offered. It’s a beautiful, heartbreaking book, a ‘must-have’ for anybody who’s ever risen to that challenge.