I’m getting on in years, so it surprises me when I learn something new regarding a commonplace of human interaction. Saying “please” and “thank you” is as commonplace as it gets. We’re told from early on that we say them to be nice. Only yesterday (and I wasn’t born yesterday) did I recognize why we really say them.

Consider two scenarios:

Scenario one: John visited Sue’s house and walked off with her flash drive. Sue asked him to return it, which he did. At that point a balance was restored. John and Sue are even now, or perhaps John still owes Sue for her trouble.

Scenario two: John and Sue are deciding what to eat for dinner tonight. John is in the mood for Japanese; Sue wants Mexican. Sue asks John to accommodate her by sacrificing his yen for Japanese, which he does. John has done Sue a favor, for which she feels indebted.

In both cases Sue makes a request and John complies, but in the first scenario John’s compliance contributes to restoring a balance on something he owes Sue. In the second John has done Sue a favor and is owed something in return.

That’s a big difference. Misinterpreting such scenarios messes up interpersonal accounting every time. In business and friendship, accounting matters. In business that’s obvious. In friendship it matters even if it’s not discussed. Friendship is founded on accounting so naturally balanced that neither party need attend to it. But if a friendship’s interpersonal accounting gets out of whack, then friends start to wonder whether they really have a friendship, and the accounting comes to the surface to be analyzed, with one party saying things like “Why do I always end up sacrificing for you?”

The other party might deny it, saying things like “That’s not true. I sacrifice for you too sometimes.” And that’s the point here. In both business and friendship there’s a kind of double-entry bookkeeping going on. Both parties keep track and the relationship stays stable so long as the tracking stays on track. If the separate records on who owes what begin to diverge it is destabilizing.

That’s where “please” and “thank you” come in. They are designed to signal a favor requested as distinct from a demand for something owed. So if Sue says “please get me the flash drive” and “thank you” when John returns it, Sue could record it as a dept paid and John could record it as a favor done. Likewise if Sue doesn’t say “please” when requesting Mexican and “thank you” when John accommodates her, she could record it as a debt paid and John could record it as a favor done. In the first case Sue would be right. In the second John would. In both cases a rift would be forming.

In their purest forms, “please” and “thank you” signal that this is a request for a favor, not a demand that a debt be paid. That’s what they are designed to represent, even if in practice they end up functioning somewhat differently. They’re supposed to be ways of acknowledging that compliance with a request is something of value for which the speaker is at least grateful if not indebted-not something the speaker is entitled to or owed.

When we’re asking a favor we should say “please” and “thank you.” When we’re owed a debt we need not and perhaps should not. In fact saying “please” and “thank you” when someone owes you blurs the very distinction these terms are designed to delineate.

And yet a couple of counterarguments are worth attention. First, you should err on the side of saying “please” and “thank you” because accommodation and obligation are very vague and relative concepts. The universe owes us nothing. We should be humbly grateful always, in fact, thankful every minute, thankful we weren’t born potato bugs. (See Dr. Seuss’ wonderful book, Did I ever tell you how lucky you are?) Even as Sue is demanding back the flash drive that John is obligated to return, she is grateful it looks like she’s going to get the drive back. For all she knows John could have taken it because his luck has been much worse than hers. He might not have been willing to return it. And there remains the argument that it’s just plain polite. A boss having hired you could just boss you around, but it’s more respectful to add “please” and “thank you,” even though you’re indebted to him for the money you’re being paid.

The second argument is that we need to say “please” and “thank you” even when we feel people are obligated to us in order to compensate for a very common tendency to treat the favors we ask for as though they were obligations owed. We want to skew transactions so as to minimize our obligations to others and maximize their obligations to us. If Sue wants Mexican and John accommodates her, Sue is then obligated to him. But if she can find a way to sneak in a moral reason why Mexican is not just a preference but the right thing to do, Sue won’t owe John anything. She may even get away with claiming John owes her something for the trouble of having to explain to him the obvious moral superiority of Mexican food.

I know, I know. It’s hard to come up with a moral principle to support Mexican over Japanese-maybe something about overfishing or the beneficial fiber content of beans. I use this ridiculous example to drive home the point. In this case it’s obvious that it’s all preference, that morality has nothing to do with it. Still, I wouldn’t put it past any of us to smuggle a little crypto-morality into even an argument for Mexican over Japanese. Rationalizing a requested favor by summoning some trumped-up moral principle is just that tempting.

Take a milder example: Suppose John likes living in a neat house and Sue (flash drive forgiven, Sue is now his partner) is more casual about it. Neither lives beyond the bounds of basic hygiene. John isn’t obsessive compulsive and Sue isn’t at risk of reviving the Bubonic Plague. Still, he’d rather she kept the place neater. Well, I wouldn’t put it past anyone in that situation to smuggle into the debate over cleanliness some rationale based not on personal preference but on what “one should do.” John could argue that “it’s better” to keep things in their place, or that it’s more “respectful,” or in his disappointment on finding the house messy (translation: maintained to his partner’s reasonable but different standard) to claim it as evidence of having been treated unfairly by some moral standard or another.

In short, we should use “please” and “thank you” selectively so we don’t confuse each other about the difference between favors and obligations, and we should use them unselectively so we show gratitude for everything and so we compensate for our natural tendency to treat the favors we ask for as though they were obligations.

And if that weren’t confusing enough we also use them sarcastically:

“Honey, pleaaasse for once will you put the dishes in the dishwasher immediately after dinner!??”

“Japanese? Are you kidding? Oh pulleeeese.”

“Finally you put the dishes away when one should! THANK you!!”

And if THAT weren’t confusing enough we use them as half-sarcasm. We put a little obligating spin on them but still feel as though we’re being appropriately humble because, after all, we did say “please” and “thank you.”

What does this morass add up to? An argument that you should be somewhat more conscientious about how these kind, useful, dangerous words get bandied about. Be a little more selective in how you use them. And be conscientious about the use of moral principles, too. Don’t claim your every preference is endorsed by some moral imperative.

I mean please, as a personal favor to me.

I mean pullleeeeeeeeez!

Thank you.