There is a personal pragmatic proof. You find that when you act on certain assumptions, things seem to turn out in a particular way, and some assumptions lead to better results than others. That’s the kind of proof that the Buddha has you act on.

"When you come to meditate you’re already acting on certain assumptions. One is that the training of the mind is worthwhile. That means you believe that your actions are important and that knowledge and training will make a difference in how you act. Those are big assumptions right there, but when you look at your life, you’ve seen that acting on those assumptions has brought you at least some happiness.

That’s called a pragmatic proof. It’s not an empirical proof. An empirical proof would be able to trace the energy that goes from our decision to act to the actual action, and from the action to the results that we experience. You’d have to run experiments with controls and actually be able to measure happiness in a very precise way. But you can’t do that. All those tests that they say they’ve run about measuring the happiness in different countries or measuring the happiness of people in different social groups, with different levels of income: When you ask people to rate their happiness on a scale from 1 to 10, what kind of science is that? What’s your 8 compared to somebody else’s 8 on a scale of 1 to 10?

So there’s really no empirical proof for any of these things. But there is a personal pragmatic proof. You find that when you act on certain assumptions, things seem to turn out in a particular way, and some assumptions lead to better results than others. That’s the kind of proof that the Buddha has you act on."

~ Thanissaro Bhikkhu "Kamma & Rebirth" (Meditations4)