The Premack Principle states that high-probability behaviors (those performed frequently under conditions of free choice) can be used to reinforce low-probability behaviors.
Whaaaat??? Don't worry, you've not only seen it, you've experienced it. When you were a child, your mom probably said, "If you eat your peas, then you can watch The Muppet Show" (yep, I'm that old).
If you do something I want, I will give you access to something you want. In the case of dog training, those are things your dog would probably do anyway, like chase the squirrels in the backyard or run up to greet visitors.
With a few environmental controls, we can withhold access to those things just long enough to use them as rewards for good behavior.
Here's an example: My dog, Parker, is a squirrel chaser. A really, really, enthusiastic squirrel chaser. When he was younger, it was almost impossible to get or keep his attention when he saw a squirrel. Now, our yard is full of squirrels. I have to let him in the yard to relieve himself and, once there, he will chase the squirrels (high probability behavior).
Since my fabulous thumbs make me the only one who can unlock and open the sliding door, I have total control over Parker's access to the backyard and, as such, access to the squirrels.
What behavior do I want more of in the presence of squirrels? I want Parker to look at me. Because looking at me is incompatible with pulling on a leash or running after a squirrel. He can't do both at the same time.
So, it goes like this: Parker sees a squirrel through the window. He runs to the slider and gives me his "HURRY!" bark. I walk to the door, to find him staring intently at his intended prey. I wait. Silently. Patiently. I have all the time in the world. Parker's the only one in a rush. He sits, but still staring at the squirrel. When he finally looks up at me I mark with a "yes" and open the door.
I just "Premacked" the attentive behavior with access to the squirrels.
Now, use the simple formula below. What does your dog want? What behavior do you want? Fill in the blanks.
Remember, anything your dog wants at any given moment can be a reward. So if your dog sees Aunt Suzie and starts pulling on the leash, and whining hysterically in his excitement, and you let him drag you all the way up to Suzie, what have you just rewarded? On the other hand, if you practice your previous training, take a few steps away from Suzie when your dog pulls, and move closer only if your dog is not pulling on the leash, you will be using access to Suzie as a reward for good leash manners.
Positive reinforcement isn't just about food. It's about smart use of available reinforcers. Use them wisely!