When boundaries are respected, they are mostly invisible. In everyday life they are the quiet architecture of our interactions, working behind the scenes to shape how we connect, cooperate, and compete. Even in the fiercest rivalry, it is the even-handed boundaries of fair play that entitle the winner to a victory that’s fair and square.
In every negotiation, boundaries are the starting point. When everyone keeps to their side of the line, talks go better and deals are more likely to satisfy both sides. But some negotiators are tempted to overstep, because a small transgression is a cheap test of how much they can get away with. Some people are less principled and more impatient, so to them a boundary isn’t a line of honour but an obstacle to move or get around. They reach for a shortcut: a clever remark, a put-down, a little pressure dressed up as well-meaning help. The more unscrupulous cross the line outright, to grab a bit more ground, whatever that ground happens to be: a tangible win, a perk, a boosted ego, or the chance to let off steam at someone else’s expense.
Putting your foot down and holding the line is the right response when someone oversteps. But the trick is knowing how to do it well. How do you tell whether someone is mean-spirited or just tired? When you set the boundary, do you fight what they said, or reframe it and refuse to let them make it about you? And then what? How will it affect the relationship, and how serious was the crossing in the first place? It usually begins small, and somewhere entirely ordinary. Like two colleagues, at the end of a long day, over a drink.
When ‘advice’ is really a crossing that leaves you worse off
Richard and Charlie had been good friends ever since they started working together. Richard saw Charlie as a bit of a maverick, one who brought real skill to the department. Charlie was ten years younger, but Richard never seemed threatened by the rising star. Every now and then they went out for a drink with a couple of other colleagues, and beyond the usual talk of work and football, they would sometimes touch on more personal things.
This time Charlie was feeling downbeat, because his girlfriend had cancelled the second weekend they were due to spend together. She was working on an important project, one she hoped would count towards her next promotion. Richard knew Charlie was serious about her, that he was even thinking of proposing. Richard felt a little irritated by his friend’s low mood, and privately thought Charlie’s girlfriend wasn’t prioritising the relationship the way Charlie was. So he said something along these lines:
‘I tell you, mate, she doesn’t really love you, you should let her go. If she doesn’t want to make the effort, that’s her choice. You know me and wifey. Sometimes we go head to head, she’s got a bit of a temper, but bless her, she spends the whole day with the kids. But I’ll tell you this much, she’s never once let me down.’
Richard’s words landed on Charlie like a ton of bricks, because suddenly he was entertaining the thought that maybe his partner wasn’t as committed as he’d believed. Something in Richard’s certainty, in the very words he chose, had sounded almost like a verdict. It left Charlie anxious, and he ended up setting the whole thing down on social media, describing the conversation in detail.
As expected, the replies split two ways. Some took Richard’s side, seeing him as a well-meaning friend who had his back. Others lectured Charlie about needing to grow up and be more supportive of his girlfriend. But somehow, none of the thirty-odd answers gave him any peace. Something about the ease with which Richard had spoken did not sit well with him. And yet now he was genuinely wondering whether Richard had been right after all.
Why well-meaning people still cross the line
Everyday life offers frequent frustrations, the boundary crossings, large and small, that happen between friends, family members and co-workers. Often enough there is no harm intended. People try to help, they offer their opinions, and they might be a bit clumsy in how they go about it, but they mean well, even when it comes packaged with a bit of entitlement. The person offering the advice thinks they genuinely know better, and that happens even when the situation doesn’t warrant the assumption. At work, Richard was the more senior of the two, but here he was borrowing that professional authority to weigh in on Charlie’s personal life. His intentions were good. He liked Charlie, and if anything he was irritated by his low mood. But he didn’t really know what was going on between Charlie and his partner. He assumed, without evidence, that it was her fault, and he applied the standards of his own relationship to a situation that wasn’t his.
But when someone delivers advice or criticism in a way that crosses a boundary, they aren’t only trying to help the other person. They are also helping themselves. Richard wanted a nice evening with his friend. Picture having a drink after a long day, wanting to unwind, and feeling that the person across from you isn’t really there. So Richard was also rushing to fix his own problem, the flat mood of his evening, and the advice came out rushed and unfiltered. What he was really saying was something like: ‘I’ve put it all out there for you, mate. Maybe she’s not the one. Accept it and move on, because we’ve got beer to drink and football to watch.’
Charlie was left perplexed. He assumed Richard’s point was about his partner. He felt the boundary being crossed, but he fixated on the surface of the message and missed what was underneath. He listened to what Richard said without ever asking why he said it that way. Was Richard really trying to make him feel better? Or was he looking forward to a relaxed evening with his friend, and now Charlie’s partner was the enemy, the one who, after all, wasn’t committed?
Why we cross the line without seeing it
And before we go further, we have to admit that Richard is not a villain. Like many people, he is overly concerned with himself and a little careless with others. As Adam Smith (1759) put it, a man of humanity hearing about an earthquake in China would be deeply moved and reflect philosophically, yet sleep soundly. The prospect of losing his own little finger tomorrow would keep him awake all night. The sympathy is real either way. The difference is whether it reaches our behaviour. A similar idea sits in the old proverb, ‘the shirt is closer than the coat.’ Our needs and interests come before other people’s. When things don’t go our way, or our interests are threatened, we feel real psychological pain. When others are affected, we feel far less, or we even choose to feel nothing.
Not because we don’t have empathy, but because empathy is expensive to run. It is effortful, it tires us, and it can be draining, which is why, given the choice, people often avoid it altogether (Cameron et al., 2019). When we can, we walk by, close our eyes, and move away from what we find distressing, uncomfortable or inconvenient. And for most of us it is enough to know we meant well, while we don’t extend the same fairness to others. We judge them by their behaviour, by what they say, not what they mean. Hence the old line, ‘the road to hell is paved with good intentions.‘
How to hold a boundary without making things worse
Now, Charlie could handle the boundary crossing in a few ways. He could snap and put it back on Richard. ‘Mate, you’re not one to talk, your wifey has you wrapped around her finger.’ But what good would that escalation do? Charlie might feel good in the moment. A bit of banter. Richard might take it lightly and move on. Or he might get offended. ‘This Charlie guy has no right to talk like that. My life is none of his business.’ Never mind the asymmetry, that Charlie’s private life had been fair game to him two seconds earlier.
The trick to setting a boundary in everyday encounters is to hold the line without making the situation worse. That is not the same as letting people off the hook, or failing to hold them accountable when the situation calls for it. But in most of our interactions, holding the line while letting the other person save face is the low-cost, low-stakes option, and usually the more effective one too. Besides, confronting someone head-on tends to be met with denial. How do you tell someone they have overstepped when, first, they believe they have your interests at heart, and second, they can’t see that they are serving their own at the very same time?
The ideal way to hold a boundary is to get the most from the least effort. So Charlie could simply say: ‘Thanks, man, but I’m good, you don’t need to be concerned.’ There’s no offence to take and nothing to argue with, and the message lands plainly: he has it sorted, and his private life isn’t up for discussion. He gets exactly what he wants, and it costs him almost nothing.
Think James Bond. A man of few words, he doesn’t complain and he doesn’t explain. He just has it handled: calm, composed, his own man, the quintessence of cool. Someone who doesn’t welcome intrusive advice keeps his autonomy without a fuss, because a strong, confident self has no fragile ego to defend and a mind of its own. Offer to ‘improve’ Bond’s life and none of it touches him. As silly as it is to borrow a film character, that’s the whole point: the steadier you are in yourself, the less effort a boundary takes.
Most of us aren’t Bond, of course, and we don’t spend our mornings chasing real villains. Charlie is one of the many of us who let other people’s opinions get under our skin, and who bristle when someone presumes to tell us what’s what. That’s ordinary and human. But the calm, low-key version is a skill you can borrow, and it works precisely because it asks so little of you.
Most people take the hint when you’d rather not talk about something, or when you don’t think they need to offer their two pennies’ worth of wisdom. So they are unlikely to push. A touch of detachment reads as a quiet step back, and people tend not to intrude on it. And as we said, it is always better to hold the line efficiently, with the least effort. But why is that so effective? Why is saying less, paradoxically, the stronger move? Because it achieves several things at once.
The Astute move: how to stop a boundary crossing by refusing the frame
When people cross your boundary, they do it because they implicitly assume their judgement is better than yours. So when they cross the line, they don’t just help, they offer you their superior idea. They solve something for you. Now, some advice is genuinely good, and I am not saying never take any. But it is rare for someone else to know what is good for you, especially when they don’t have the full picture. So by not engaging, you don’t just reject their framing, you don’t open the negotiation at all. You disqualify the attempt before it starts. Above all, it is an Astute move. You see that the real frame is often not the topic they are advising on at all. The thing being served is their need to know better.
Once you allow it, a crossing can be expensive. Charlie let Richard frame his relationship in a negative light, and that smudged his own thinking. If Charlie had held the line, he would have kept the space to weigh his own situation, to see whether his priorities and his partner’s really aligned, and perhaps to decide that it was not unreasonable for her to prioritise other things sometimes. Instead, the crossing threatened something deeper than his need to be right. It destabilised him, and pushed him to judge his relationship by running a little experiment on social media, asking strangers for their opinions. Left unguarded, a boundary crossing cuts deep. Richard’s words, accepted at face value, started to carry weight. He suddenly began to suspect that his partner was not committed, because Richard had planted a doubt that was not there before. Was Richard evil, or even ill-intentioned? Most likely not.
The Psychopomp: why the dig is about them, not you
But in other situations, driven by envy or resentment, or in high-stakes business deals, less orthodox negotiators will attack people’s worth, well-being and security. Why? Because someone who is destabilised is more likely to spiral into bad decisions, make concessions, and give more. The defence is to guard your self-esteem and your peace of mind. Your worth is not on the table. When unprincipled dealmakers offend you, frighten you, throw accusations or paint doomsday scenarios, even unfounded ones, your brain might treat them as real, though the evidence for them is thin. And a threatened ego fights to save itself, not the deal. So the answer to a boundary crossing is to stand your ground emotionally. When Charlie said, ‘Thanks, man, I’m good,’ that ‘I’m good’ meant he was fine, he was grounded, and he would think about his relationship in his own time and of his own accord.
Refusing to let someone cross a boundary is refusing them access to your inner life. High-stakes dealmakers don’t only negotiate financial terms. They also work on your intentions, your needs, your motivations, your sense of worth. So it pays to keep one eye on the deal in front of you and one on what sits beneath the surface. Don’t let them get under your skin. The Psychopomp capacity, the intuitive one, is to understand what really drives people when they get personal, so the dig lands on the motive and not on you. Sometimes it’s money, sometimes it’s ego, sometimes it’s something as small as wanting a nice evening. Richard got personal because he was frustrated with his friend. He dismissed Charlie’s feelings and rushed him towards accepting that his relationship was doomed.
The Mediator: how to hold the line and keep the relationship
And once you can see clearly that a boundary was crossed, what do you do with it? You notice the other person was careless, unconcerned, maybe a little selfish. Where does that leave you? How do you see the relationship going from here? Because the way you hold the boundary also negotiates the relationship. A crossing can breed doubt and defensiveness, as it did in Charlie, but it can also trigger a fight-or-flight reaction. Some people snap: ‘Mind your own business!’, ‘Your wife is not a career woman like my partner!’, ‘I want to support her dreams, I’m not worried about her prioritising work now and then!’ Some comebacks are outright confrontational, rude, or risky. And, as we asked earlier, what good do they do? Sometimes you do need to say what you think, even when it isn’t pleasant. But a relationship worth preserving is worth handling with a little caution.
If staying cool was hard for Charlie, he could have said something like, ‘Ha, appreciate it, but I’m good, she’s worth it.’ Brief, warm, and it closes the topic without a debate. No dig at the choice to be a stay-at-home mum, no competition between two perfectly reasonable ways to live. Or he could have gone further: ‘Thanks, Rich, but honestly it goes both ways. I’ve had my share of late finishes, and I’ve cancelled plans a good few times myself, so I can’t really complain.’ That quietly reframes the cancelling as a two-way street. Or he could have explained: ‘Look, Rich, I know you have my back, but this really matters to her. I’m there to support her, and it’s not like her to change plans last minute.’ While it’s usually better not to have to explain yourself, sometimes you want to hold the boundary and tend the relationship at the same time. When you’re dealing with a valued partner who is occasionally clumsy or a bit selfish, you can still hold the line. The trick is to acknowledge their point of view, concede 10%, and hold your main point. Why does it work? Because someone who makes a small concession can’t be accused of being unreasonable, and it leaves the other person feeling heard, never mind that their opinion was a little misplaced.
So you can mediate the relationship and handle the crossing with care, because a good relationship is a bridge you want left standing. You can understand people and their behaviour without agreeing with them. As long as the crossing is a one-off rather than a pattern, as long as it doesn’t violate your real interests or the deal itself, and as long as there’s no intent to harm, it’s better to work with people than against them. Choosing the relationship over the occasional faux pas doesn’t mean betraying your principles, or keeping someone around in case you need them later. Relationships aren’t governed only by the psychological traits of the people in them, but also by social mechanisms. Think of reciprocity: I help you, you help me. Or grace: I let this faux pas go, and you let me off the hook another time. Or the simple importance of letting someone save face, because maybe they overclaimed, got carried away, or were just too enthusiastic, angry, or nervous. The Mediator’s move is to look at the social rules that govern how people deal with one another, the prescribed norms of interaction and behaviour in a society. Why? Because most of us, whatever our psychological make-up, live by them.
The Mediator’s move in negotiation is to find common ground, to keep both parties on equal footing, with some healthy give and take. What keeps the Mediator from being taken advantage of is the capacity to recognise when someone is using the social ties of a relationship to hurt or exploit.
The Hermaion. How to recognise when a crossing becomes a pattern
Now imagine yourself a fly on the wall in Richard and Charlie’s office. A couple of days after the insensitive comment, Richard starts teasing Charlie by calling him Romeo. He seems to mean it light-heartedly, but he drops it in front of two other colleagues. ‘Romeo here will deliver your report by Monday.’ Charlie’s deadline is actually Tuesday. Richard is framing him as love-struck and doomed to fail. Charlie barely flinches. His technical skills are outstanding, but away from the things he’s good at, he struggles to set boundaries. If Richard wanted to solve a technical problem the wrong way, Charlie wouldn’t hold back for a second, he’d know exactly what to say. But when things get personal, he feels annoyed and powerless at once, and he overthinks it. ‘What would I even say? What can anyone say? That’s just how Richard talks.’ What Charlie doesn’t know is that at the last conference call, the director had praised him warmly, right in front of Richard. ‘Rich, I must say, you’re lucky to have Charlie. Since he joined your team he’s really made a difference.’
A one-off faux pas did not make Richard a villain, and that first comment was the kind of crossing you work with. But this is a different thing entirely. When the digs settle into a pattern, you have to ask whether something more is going on. Why has Richard suddenly changed his attitude towards Charlie? And what is he banking on when he takes the liberty of talking like that? He knows Charlie is loyal and rather serious, so he isn’t expecting him to fire back with something witty or cutting. That is exactly why Richard feels safe to dig: he is holding Charlie hostage to their relationship, using the friendship itself as the thing that keeps Charlie quiet. He is exploiting Charlie’s goodwill.
When a boundary crossing turns adversarial, the point is no longer just to defend the boundary but to make the crossing expensive. Ordinarily it’s healthy to give the other person the benefit of the doubt and to stay a bit cool. But a boundary left unattended can slowly erode your self-confidence and your good mood. Repeated digs are trying to paint you a certain way, and repeated messages stick, even when they’re untrue. That is how propaganda works: say something false often enough and people stop questioning whether it’s true, a pattern psychologists call the illusory truth effect (Hasher, Goldstein, & Toppino, 1977). Words stop being just words. They become what someone makes of you, and how they manage other people’s perception of you. So when a boundary is crossed again and again, the cost of defending it is justified, because the alternative is to let a bully win.
Usually the grey rock method works by ignoring the comment, or refusing to give a bully’s joke any importance. Without the positive reinforcement of seeing the target visibly upset, the bully may simply move on. The danger is staying quiet when the bullying is personally motivated and fairly relentless, because then people sometimes double down, precisely in the hope of getting a reaction. Grey rock works when the water isn’t constantly washing over you, but if you let the waves keep breaking, they wear you down into a smaller, more convenient version of yourself.
How to make a crossing expensive
So how could Charlie make Richard’s comments expensive? By levelling the playing field. The cleanest move is the one that exposes the real motive, because Richard’s whole cover is that this is just banter. ‘No need to get jealous, Rich, ha!’ does it in just a few words: it names the envy, imposes the cost of being seen through, and the ‘ha!’ keeps it deniable. A lighter version simply hands the label back: ‘Rich, it takes one to know one, you were a golden retriever back in the day.’ Or Charlie can make the cost quieter and still real: ‘Deadline’s Tuesday, by the way. But I appreciate the vote of confidence, Romeo and all,’ which corrects the little power-play and owns the nickname, and owning a nickname deflates it. Or, quieter still, ‘You’ve been on the Romeo thing a while now, Rich. Everything alright?’, which turns the concern back on him and exposes the pattern without a single insult.
Charlie could also play dirty. ‘I hope you and the wife still have a good thing going.’ It lands, but it costs him something. The marriage jab makes Charlie do the very thing he resented Richard for, reaching into someone’s private life. Playing dirty is an option, but not the first one to reach for. Besides, Richard’s digs work precisely because he keeps plausible deniability. If Charlie comes back openly nasty, Richard can turn around, wide-eyed, and say, ‘Wow, man, that’s rich. I didn’t see that coming from you.’ Just like that, Charlie is the villain. This is the move called DARVO: deny, attack, and reverse victim and offender (Freyd, 1997). Standing on higher ground is more likely to pay off, even when the other side plays dirty. It keeps your hands clean, it leaves them nothing to throw back at you, and it holds them accountable.
A boundary crossing is almost never truly random. Only very rarely do we ramble, lose the thread, and land by accident on a sore spot. ‘Hmm, I’m not a cat person myself, there’s something shady about people who like cats. Oh no, I forgot your cat died three years ago!’ Some people have less social awareness than others, but on the whole we don’t stumble into insults by chance. People will blame a slip on being tired, on a bad day, on being grumpy, on one too many drinks. But as the saying goes, in vino veritas: the wine tends to speak the truth the person was holding back. Or there’s ‘it was only a joke’, the classic reach for plausible deniability. At the royal court, the jester got away with all kinds of mischief because he could deliver hard truths as jokes, but even he had to watch how far he took it. And frustrating as it can be, we still hand people the benefit of the doubt. That is a gift, a gesture of goodwill, because we don’t yet know whether it will become a pattern.
Being generous without being taken advantage of
If someone is repeatedly rude or intrusive, they are not just having a bad day. They want something out of you. It might be something tangible, like better terms in a deal, or a secondary gain, like propping up their ego at your expense. Maybe they carry an inferiority complex and feel taller when they belittle others. Or maybe they’re stressed, they cast you as lower in their imagined pecking order, and you become the one who has to metabolise their stress. Passing the ulcers down the line, as Sapolsky would fittingly put it (Sapolsky, 2017). Whatever it is, watching the crossing repeat is what puts it in perspective. Frequent transgressions, the digs, the hurtful comments, the unwanted criticism or advice, all signal that you are on the receiving end of unbalanced relationships. You are the safety net for other people’s egos and their stress. You are a giver.
There is nothing wrong with being generous, and being nice doesn’t have to leave you open to boundary violations. As a society, we all benefit from other people’s generosity. Unpatented vaccines have saved millions of lives. In 1955, when the journalist Edward R. Murrow asked the virologist Jonas Salk who owned the patent on the polio vaccine, he replied, ‘Well, the people, I would say. There is no patent. Could you patent the sun?’ (Salk, 1955, as cited in Retro Report, n.d.). Many would say access to life-saving medicine is a right, and the researchers who chose not to patent theirs are part of why. But there is a real difference between doing something for the greater good, for a noble cause, and letting the taker beside you profit from your generosity of spirit. A depleted person achieves less, not more. Someone running on empty because they are always listening, absorbing stress, and solving other people’s problems has less left for what is meaningful in their own life. So the boundary is not about giving less. It’s about being selective, directing your energy towards the causes and people you choose, and sanctioning those who exploit it.
When a favour becomes an expectation
The Hermaion capacity takes the long view: over time, what does a small concession actually cost? Because a boundary isn’t only lost when someone crosses it. It can also be given away, a little at a time, one small yes after another.
Imagine now that Charlie has a new colleague, Jack, who recently moved to the city. Jack is switched on, smart, and very forward. Chatting with Charlie, he discovers they live in the same neighbourhood. ‘No way, man! You live literally five minutes from me! And I’m thinking, would it be too much trouble to give me a lift on the way home? Be great to have someone to talk to about the good places in town, all that.’
Say Charlie agrees. In rush hour the drop-off runs longer than five minutes, so the extra mile is really an extra ten minutes a day. That’s about an hour a week, four a month, over forty hours a year, a whole working week. Charlie might think he’s gaining a friend, an ally, someone nice to talk to. But often enough a small favour becomes an expectation. Some evenings he hangs back fifteen extra minutes waiting for Jack to finish a task; other times he feels uneasy about telling Jack he needs to work late. Two weeks in, Charlie already regrets it. And Jack loves to gossip, deep into office politics: ‘What do you make of Ray, the new starter? Gets on my nerves. Talks like he’s some kind of genius. Maybe he’s good, but whatever, man.’ Now the ten minutes isn’t just time. It’s a daily dose of someone else’s grievances, and Charlie is a captive audience.
The Hermaion capacity in negotiation can manage the exit: the setting of the boundary. A goodwill gesture can quietly become the new status quo. Today’s favour is tomorrow’s expectation, as someone I knew used to say. Now Charlie needs to handle this with Jack, and frame it in a way that doesn’t give Jack an easy way to push back. Charlie could say, ‘I feel bad keeping you hanging around until I finish work,’ and Jack might reply, ‘No problem, man, I don’t mind waiting.’ Or Charlie might try, ‘The traffic on the way back is tricky,’ and Jack might guilt-trip him: ‘I didn’t think it was that bad. I wouldn’t have asked you for the favour in the first place, but really, whatever you say, it’s your time, never mind me.’ So the boundary needs a good frame, something Jack can’t object to, while Charlie stays warm and polite. Something along the lines of: ‘Sorry, Jack, I’m going to stop the regular evening lift, the time adds up and I need my evenings a bit more flexible. Nothing personal, mate, I’ve enjoyed the company.’ The flexibility is the solid, real reason, and the time adding up sits behind it, giving it a bit more weight. Now Jack might just say, ‘I see, no problem, mate,’ or he might say, ‘Oh, I see, I was looking forward to our evening commute.’ So even a well-enforced boundary is not always free of guilt, and that is simply how it is.
Notice the exit isn’t the Hermaion alone. Charlie frames it so Jack can’t object, the Astute. He stays warm to keep the friendship, the Mediator. He holds his line against the guilt, the Psychopomp. Hermaion gathers the other three and walks them to the door.
Pick your battles, hold your ground, keep your peace
To sum up, negotiating a boundary crossing begins with perspective: is it doing real damage, or is it just an inconvenience? Is it a repeated dig, or a one-off? An isolated incident can still sting in the moment, but it rarely needs any special response. We all have to choose our negotiations the way we pick our battles, because none of us has unlimited energy to attend to and shape every passing interaction, and that is fine. What we do need is to be present and prepared when a crossing is aimed at something real: a tangible win, a perk, a secondary gain, or even the chance to offload someone’s own anger, anxiety, or discontent onto us.
Once you’ve concluded that a crossing is more than casual carelessness, you set the boundary, and you do two things at once: you hold your ground, and you make the transgression expensive. In each case the move is the same: you reframe what they said and put it back on them, instead of taking it on yourself, whether by naming the behaviour, asking them to explain what they meant, turning it into a light-hearted joke at their expense, or even digging back, if you’re willing to burn the bridge. Often enough people take the message, and once they realise you won’t be on the receiving end of their jokes or their malice, they retreat. But every now and then you’ll meet someone who makes a sport of it, who relishes a fight with anyone available and willing to engage. There, wisdom beats cleverness: pocket the witty comeback you had ready, and take the high road. Not because you couldn’t put them in their place, but because in the grand scheme of things you’d win nothing of substance, and your life holds far more important things to do.
References
- Cameron, C. D., Hutcherson, C. A., Ferguson, A. M., Scheffer, J. A., Hadjiandreou, E., & Inzlicht, M. (2019). Empathy is hard work: People choose to avoid empathy because of its cognitive costs. Journal of Experimental Psychology: General, 148(6), 962–976. https://doi.org/10.1037/xge0000595
- Freyd, J. J. (1997). Violations of power, adaptive blindness, and betrayal trauma theory. Feminism & Psychology, 7(1), 22–32. https://doi.org/10.1177/0959353597071004
- Hasher, L., Goldstein, D., & Toppino, T. (1977). Frequency and the conference of referential validity. Journal of Verbal Learning and Verbal Behavior, 16(1), 107–112. https://doi.org/10.1016/S0022-5371(77)80012-1
- Retro Report. (n.d.). Could you patent the sun? [Video transcript]. https://retroreport.org/transcript/transcript-could-you-patent-the-sun/
- Sapolsky, R. M. (2017). Behave: The biology of humans at our best and worst. Penguin Press.
- Smith, A. (1759). The theory of moral sentiments. A. Millar.