It's not uncommon for me to hear people say" I don't want to use food to train my dog. He should do it because he respects me and I praise him".
I would like you to take a moment and think of people in your life. Who do you respect? Who do you do things for happily, willingly? Why?
Do you respect a person just because they demand it? Do you respect the boss who demands you work late, and then doesn’t recognize the extra effort you put in? If you had a choice, would you still do the work – just because he asked, without compensation?

I am not one to compare my dog to a human all the time and I try to not anthropomorphize behaviour (attribute human characteristics). There have been many advances in the studies of dog behaviour over the past few years giving us a clearer picture of dogs and dog behaviour. All you need to do is look around a bit – Dr. Alexandra Horowitz, Dr. Roger Abrantes, Dr. Adam Miklosi, Dr. Ian Dunbar, to name a few.

Motivation, as defined by Miriam Webster dictionary: 
“The act or process of giving someone a reason for doing something”
“The condition of being eager to act or work”
“A force or influence that causes someone to do something”

No matter how you spin it, it boils down to having a reason to do something - motivation. Any sentient being (as defined by Miriam Webster dictionary - the ability to feel, see, hear, smell or taste) is likely to do something because they are motivated to do so.
If you want to remain alive, you are motivated to survive.

Food; nourishment, sustenance – without it I don’t think any species would survive. I am not a biologist, so perhaps there is something out there that works differently. I don’t know. For dogs and humans – it’s essential.
Food is a primary reinforcer (a biological need crucial for survival – no learning is involved). Secondary reinforcers are things which have been paired with or associated with a primary reinforcer. They require learning.

Your dog likes liver (food is a primary reinforcer). 
You want him to offer his paw. The act of offering his paw has no value whatsoever to your dog at first. There is no reason for him to do it.
You give your dog a piece of liver every time he offers his paw. After a few repetitions, your dog  learns to offer his paw because it results in a piece of liver. He is motivated to offer his paw more frequently.

Praise: my dog should work for “good boy” and nothing more.  You stay late at work to get a job done because your boss asked you to. In the morning, you hand it in, he pats you on the back, says, thanks, and walks away. You likely are standing there, open mouthed, possibly cursing in your head (or out loud) feeling taken advantage of and under valued.

Praise can be reinforcing if it’s been paired enough times with a primary reinforcer, such as food. I say “good dog” and every time I do, I give my dog liver. Over time, the phrase “good dog” elicits the same emotional response as the liver alone. 

Nobody works for nothing. Even those who volunteer, do so because they are intrinsically motivated.

How many would be motivated to go to work each morning, if there was no cheque at the end of the week? Do you go in because you respect your boss? Or do you go everyday because your boss writes the cheque and the cheque allows you, at it’s most basic function, to feed your family, yourself and provide shelter?

When people say their dog isn’t motivated by food, I ask “does your dog eat?”.