The 17th century philosopher Blaise Pascal is perhaps best known for Pascal’s Wager which, in the first formal use of decision theory, argued that believing in God is the most pragmatic decision. But it seems the French thinker also had a knack for psychology. As Brain Pickings points out, Pascal set out the most effective way to get someone to change their mind, centuries before experimental psychologists began to formally study persuasion:

When we wish to correct with advantage, and to show another that he errs, we must notice from what side he views the matter, for on that side it is usually true, and admit that truth to him, but reveal to him the side on which it is false. He is satisfied with that, for he sees that he was not mistaken, and that he only failed to see all sides. Now, no one is offended at not seeing everything; but one does not like to be mistaken, and that perhaps arises from the fact that man naturally cannot see everything, and that naturally he cannot err in the side he looks at, since the perceptions of our senses are always true.

Pascal added:

People are generally better persuaded by the reasons which they have themselves discovered than by those which have come into the mind of others.

Put simply, Pascal suggests that before disagreeing with someone, first point out the ways in which they’re right. And to effectively persuade someone to change their mind, lead them to discover a counter-point of their own accord. Arthur Markman, psychology professor at The University of Texas at Austin, says both these points hold true.

“One of the first things you have to do to give someone permission to change their mind is to lower their defenses and prevent them from digging their heels in to the position they already staked out,” he says. “If I immediately start to tell you all the ways in which you’re wrong, there’s no incentive for you to co-operate. But if I start by saying, ‘Ah yeah, you made a couple of really good points here, I think these are important issues,’ now you’re giving the other party a reason to want to co-operate as part of the exchange. And that gives you a chance to give voice your own concerns about their position in a way that allows co-operation.”

Markman also supports Pascal’s second persuasive suggestion. “If I have an idea myself, I feel I can claim ownership over that idea, as opposed to having to take your idea, which means I have to explicitly say, ‘I’m going to defer to you as the authority on this.’ Not everybody wants to do that,” he adds.

In other words, if it wasn’t enough that Pascal is recognized as a mathematician, physicist, and philosopher, it seems he was also an early psychologist.