Why does a promise bind, when breaking it would cost us nothing and no one would find out?
There is a particular kind of promise that has no enforcement behind it at all.
We told someone we would do a thing. They have since forgotten. Nobody else heard. There is no record, no consequence, no chance of discovery, and doing it will cost us an afternoon we do not have. If we quietly didn't, the universe would register nothing.
Most of us do it anyway. And if we don't, we feel something, which is the strange part — a small private accusation from a source we would struggle to name.
I have never been able to explain to myself what exactly was created when I said the words.
Think about how odd promising is as a mechanism.
Nothing moves. No money changes hands, no object is transferred, no law is invoked. Air is pushed past a tongue in a particular pattern, and afterwards an obligation exists that did not exist ninety seconds earlier. We do this several times a day and never find it remarkable.
The law, which we might expect to be confident here, is markedly less confident than we are. Under common law a bare promise — a promise with nothing given in exchange — is generally not enforceable at all. There must be consideration, a bargain, something moving the other way, before a court will treat our words as binding.[^consideration] Which is a quiet admission: the legal system does not believe words alone can create an obligation. It believes a trade can.
And yet in ordinary life we behave as though words alone do exactly that. The promises we feel most bound by are almost never the ones with consideration behind them.
The best account I know is the strategic one, and it deserves to be stated at full strength rather than waved at.
Thomas Schelling's insight, which reshaped how economists think about bargaining, is that the ability to bind our own hands is a form of power.[^schelling] A driver who visibly rips out his own steering wheel wins the game of chicken. A negotiator who has publicly committed to a number has, by giving up his freedom to move, gained leverage. On this reading a promise is a commitment device: it is valuable because breaking it is expensive. Reputation is the enforcement mechanism, and the cost is what makes the signal worth anything.
This explains an enormous amount. It explains why we want promises made in front of witnesses. It explains our particular fury at the person who breaks small promises casually — he is showing us the cost is low for him, which is exactly the information we needed. It explains why a promise from a stranger passing through town is worth less than the same words from a neighbor.
What it does not explain is the promise in the first paragraph.
There the whole apparatus is missing. No witnesses, no reputation at stake, no repeated game, no future encounter in which today's behavior could be priced. And it is not a marginal case. People keep promises made to the dying. People keep promises to parents who have been gone for decades and could not be disappointed if they tried. A man will drive four hours to put flowers somewhere because of something he said to someone who is no longer there to know whether he did it.
On the strategic account, keeping that promise is simply an error. The habit was built for live bargaining, where there is someone across the table who can hold us to our word, and here it goes on running long after the other party is gone. Maybe that is all it is. But it is a remarkably consistent error, and from the inside it does not feel like one. It feels like the thing is still owed.
Lewis B. Smedes, who spent a good part of his life thinking about this, put the matter the other way round. A promise, he argued, is how a creature who cannot control the future reaches into it anyway and makes one small patch of it dependable — and in doing so becomes someone with a shape that outlasts his moods.[^smedes] On that reading the promise to the dead is not a leftover habit running on. It is a person being the same person.
There is a small 1994 film that puts the question about as plainly as it can be put, It Could Happen to You.[^film] A New York cop tells a waitress he will split his lottery ticket with her. The ticket then wins four million dollars, and his wife explains to him that the promise cannot possibly count, since nothing was ever written down — which is very nearly the common-law position, and is still obviously the wrong answer. He goes back and hands over two million. The money turns out to be the least interesting thing in the picture. The wife keeps becoming a different person as the circumstances move, grasping while there is something to grasp and lost when there isn't; the cop, who has just paid an absurd price for one sentence nobody could have held him to, is the only person in the story who still knows who he is. The promise did not merely bind him. It held him together.
Say that plainly, though, and it cuts both ways. A promise we will not break can end up as the last load-bearing wall of a self we are constructing — the one beam still upright in a house held up entirely by our own performance, and therefore the one we cannot afford to let go of. That is an enormous weight to hang on a sentence said to a waitress. An identity we build has to be defended everywhere at once, and every promise gets conscripted into the defense; an identity we are given does not need defending, because nothing we keep or fail to keep is holding it up. Only the second kind can carry that load without cracking.
There is a way this goes wrong, though, and it is worth naming before we go on. Keeping our word is exactly the kind of thing that turns into a righteousness project. The promise stops being about the person we made it to and starts being about the record we are assembling — evidence that we are the sort of person who follows through, filed against an accusation nobody has actually brought. That may be part of why the small private accusation is so hard to place. Some of it is conscience. Some of it is the ledger. And a promise kept to keep the ledger clean is not much of a gift to anyone; it is a payment, and the person we made it to is incidental to it. Whether anything can relieve us of the ledger without also relieving us of the promise is a question I could not answer for a long time.
The answer, when it finally came, was that the ledger has already been settled, and not by us. The record we keep trying to assemble is finished — the record of debt that stood against us was cancelled and nailed to a cross, and the verdict on us came in before we ever made a single promise. No promise we keep adds a line to it. No promise we break subtracts one. That does not dissolve our word; it hands it back to us. Relieved of having to prove anything about the person who said it, a promise is finally free to be about the person we gave it to.
There is a second place the strategic account runs thin, and it is closer to home. We make promises to ourselves. Not resolutions, which are forecasts and behave like forecasts — actual promises, of the kind a person will honor at real cost years later because they said so once. There is no counterparty at all there. No one to lose face with, no one to defect against. Whatever is doing the binding is not doing it between two people.
I think the confusion underneath all of this is that we have started hearing vows as forecasts.
Say the words I will love you for the rest of my life in the modern ear and they scan as a prediction — a sincere estimate about future feeling. Which means that when the feeling changes, nothing has been broken. We were simply wrong about the weather. People end things now with real bewilderment at being blamed: I meant it when I said it. And they did.
But a vow was never a forecast, and we can tell by noticing when it does its work. Nobody needs a promise for the stretch where they want to do the thing anyway. The promise exists for the other stretch. Its entire function is to govern the case where the feeling has gone — which means a vow understood as a prediction about feeling has been emptied of the only thing it was for.
This is not an argument that people should stay in ruinous marriages, and it would be dishonest to let the logic slide there unremarked; a vow can be broken by the other party long before anyone files anything, and Scripture itself knows about covenants already destroyed from the inside. The narrower point is about what was being said in the first place. A promise that only holds while the feeling holds was never doing any work — it was describing a mood and borrowing the grammar of an oath.
So the question underneath why does a promise bind turns out to be a question about what kind of thing a person is. If we are essentially a sequence of states, then a promise is one state trying to tyrannize the ones that follow, and it should lose. If we are something that persists — something that can be the same across time in a way that makes the person who spoke and the person who must now pay genuinely one person — then a promise binds, and the binding is not tyranny. It is just identity, holding.
And then the question turns once more, because our own persistence is not the bottom of it. We did not invent promising, and we are not self-originating creatures who happen to endure. We are made in the image of a God who binds himself — who puts his own name behind a word and then stands by it toward people who have no power whatever to hold him to it, no court to appeal to, no leverage, nothing to offer the other way. That is why air pushed past a tongue can bind at all. Promising is not a clever device we stumbled into for strategic reasons; it is a family resemblance. And the absurd price for one sentence nobody could have enforced has already been paid in full, once, by someone who went to a cross rather than go back on what he had said.
The sharpest statement of that I know was written for the stage, and given to a man a few weeks from the scaffold. In Robert Bolt's A Man for All Seasons, Thomas More is in the Tower for refusing an oath, and his daughter Meg has come to argue him out of it. She loves him, she wants him alive, and her case is a good one: say the words, mean none of them, God listens to the heart and not to the tongue. Take the oath and come home. He answers her like this:
> "When a man takes an oath, Meg, he's holding his own self in his own hands. Like water. And if he opens his fingers then — he needn't hope to find himself again."
There is no rule being obeyed there and no reputation being guarded. Nobody in that cell is keeping score, and the only audience is a daughter pleading with him to stop. The self is the thing in his hands. He is not merely refusing to lie about God; he is refusing to spill himself. And what makes the image so exact is how quiet the loss would be — he does not have to throw anything away. He only has to relax. Water never needs to be poured out. It needs fingers that open.
But water held in a man's own hands is a hard place to leave the matter, and I do not think it is where the matter ends. Fingers tire. Mine do. If our promising holds at all, it is not finally because our grip is good — it is because there is an older oath underneath it, sworn by someone who had no one greater to swear by and kept at his own expense. What we are doing when we keep our word to the dead is less a feat of strength than an echo. And the oath I mean was sworn in the dark, over a sleeping man, which is worth going back to look at.
The ancient world had a form for this, and it is considerably more serious than a handshake.
In Genesis 15, Abram is told to bring animals, cut them in half and lay the pieces opposite each other with a path down the middle.[^gen15] No explanation is given in the text, and for a long time I read past it as one more piece of strangeness.
The explanation comes centuries later, in Jeremiah 34, where God indicts men who broke his covenant and says he will make them "like the calf that they cut in two and passed between its parts."[^jer] That is what the aisle was for. The parties to a covenant walked between the halves of the slaughtered animal, and the walk was a sentence spoken with the feet: may I be made like this if I break faith with you. A promise with the penalty acted out in advance.
Now go back to Genesis 15 and watch who walks.
Abram doesn't. A deep sleep falls on him, and a dreadful darkness, and while he is unconscious a smoking fire pot and a flaming torch pass between the pieces alone. Only God walks the aisle.
Which is a staggering arrangement if we take the ritual seriously. Two parties are entering a covenant. One of them cannot break faith. The other one demonstrably will, repeatedly, for the entire rest of the book. And it is the first who takes the self-curse, while the second is asleep in the dark and cannot even watch.
I should say where this way of reading comes from. The instinct to stop at a covenant scene and ask who walks the aisle — and, more generally, to ask what a passage does to the heart rather than what it demands of the hands — I learned from Tim Keller. A great deal of what I notice, I notice because he taught me where to look. I can't point you to a sermon for this one; the debt is older and broader than a footnote.
There is a further oddity I had never thought to ask about.
Hebrews 6 notes that when God made his promise to Abraham, "since he had no one greater by whom to swear, he swore by himself." Set aside the logic problem for a moment and ask the practical question: why swear at all? An oath adds nothing to the word of someone who cannot lie. A God who is already faithful does not become more faithful by raising his hand.
Hebrews answers it, and the answer is not about him. He swore, the writer says, because he wanted to show the heirs of the promise how unchangeable his purpose was — so that we would have something to hold. The oath was not needed at his end. It was added at ours. He did the one thing that was strictly unnecessary for him and absolutely necessary for us, which is more or less the shape of everything else he does.
And then Hebrews reaches for exactly the image we need, because it is the reverse of water in a man's hands. It calls the promise an anchor for the soul. Not something we hold — something that holds us, and holds hardest at the moment we have stopped being able to grip anything at all.
So that small private accusation, when we think about quietly not doing the thing nobody would ever know about, may be less a ledger than a likeness. We keep our word in the dark because we come from someone who walked the aisle alone in the dark, over a sleeping man who could not even watch, and who has never once opened his fingers.
[^consideration]: On the requirement of consideration for an enforceable promise, see Restatement (Second) of Contracts § 71 (1981). [^schelling]: Thomas C. Schelling, The Strategy of Conflict (Harvard University Press, 1960), ch. 2. [^smedes]: Lewis B. Smedes, "Controlling the Unpredictable — The Power of Promising," Christianity Today, January 21, 1983. [^film]: It Could Happen to You, dir. Andrew Bergman (TriStar, 1994). [^gen15]: Genesis 15:9-10. [^jer]: Jeremiah 34:18-20.
[^heb]: Hebrews 6:13–18. [^gal]: Galatians 3:13, citing Deuteronomy 21:23.