The two university students, close friends, had hooked up before. They lost their virginity to each other early in first year, not long after meeting at a residence mixer during frosh week. The sex always happened under the same circumstances: They were out partying, drunk, and stumbled home together, a friend-with-benefits scenario. They didn't talk about it the next day, except to say, "Are we good?" and "Yes, we're good," and they didn't really tell anyone to avoid the assumption they were in a relationship.

But after a while, the female student (who has asked not to be identified in this story) began to feel uncertain about the assumptions underlying their hookups. During a week of alcohol-centred activities at McGill University that winter – "a shit-show for consent," as she puts it – her friend convinced her to do the annual Mountain Run, in which teams race to the top of Mount Royal while chugging beer and slamming vodka shots. "I was puking the whole way," says the female student looking back on her freshman year. But back in his room, they were snuggling, and things started to progress. She didn't really want to have sex, she says, and she was pretty drunk. "We'll do it fast," she recalls him saying. "And I said, 'Well, okay.' " Looking back, she says, "We should have talked more. I should have been more willing to assert myself."

Was it consensual? Was it assault? Her story highlights how fraught and complicated those questions are, especially in the early weeks and months of university, a period known as the Red Zone, when the risk of sexual assault is highest, especially for first-year students. Two decades after No Means No began to gain traction in the debate over what constitutes consent, a new wave of students and educators are flipping that message around – and insisting coeds (i.e. mainly men) take responsibility by asking for a "Yes." It's a deceptively simple tweak, one that the State of California passed into law in September, to great controversy.

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Ratcheting up the public conversation about the definition of enthusiastic consent, it energized campaigns oriented around the Yes Means Yes message on campuses across North America. They included an October #getconsent social-media blitz at Dalhousie University in Halifax; an "Ask, Listen, Respect" campaign at McGill; a September university-wide panel on sexual communication at Concordia in Montreal; and ongoing "Consent is Sexy" messaging at a number of universities.

Students' first term on campus is not only a time of lectures and learning, but also a time when crowds of relatively inexperienced teenagers are set loose in a party culture saturated with alcohol and expectations of easy hookups. It's a perennial problem on campuses: The orientation-week chants that caused controversies at several Canadian universities last year for promoting sex without consent aren't new – a collection of misogynistic ballads has floated online for years. Among them: a little gem called The Gang Bang Song. (Sample lyric: "I love a gang bang. Oh, yes, I do.")

A U.S. study in 2007 found that 50 per cent of sexual assaults happen between August and November. There aren't good Canadian Red Zone stats, because universities aren't required to publicly report sexual-assault complaints. But we do know this: At least one in five women say they have experienced sexual assault that includes penetration by the time they graduate, according to University of Windsor researcher Charlene Senn, who studies rape prevention; if you include unwanted touching or being "coerced" into sex, she says, the rate rises to more than 50 per cent. The vast majority of victims never go to the police, and cases that do get reported rarely result in convictions.

Two decades of No Means No didn't solve the thorny problems surrounding consent. The slogan, first coined by the Canadian Federation of Students, was stamped on campus posters and nightclub coasters, and chanted at rallies across North America. But it never worked as well as educators and feminists hoped. The words were fierce and memorable, but criticized for keeping the onus on women to halt unwanted sex – even as Canada's Criminal Code and Supreme Court established affirmative consent as the legal standard.

Yes Means Yes, by contrast, takes the focus off of listening for a "No," and tells coeds to ensure they have an explicit "Yes." California's law was the first of its kind in North America, requiring state universities investigating sexual-assault complaints to define consent as an overt, clear "yes." Critics quickly decried it as overkill, saying that the law criminalized an unsolicited kiss between couples – as if the jails would soon be crowded with loving, smooch-sneaking partners.

Advocates say that it frames sex more positively, shifting the focus from what a victim did (or didn't do, or couldn't do) to the steps a perpetrator failed to take to pro-actively ensure consent. An enthusiastic "yes" must become the new bar by which consent is measured, those advocates maintain, arguing that body language can be easily misinterpreted, especially when one or both parties are intoxicated, and cannot constitute consent.

Still, it's a tough sell: convincing young people to do the asking – not just once, but throughout their sexual encounters. And beyond the back seat and the bedroom, it has stirred broader questions: Will it help shift our collective conversation about sexuality? And will it make campuses safer?

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'A weird, steep learning curve'

More than 90 per cent of sexual assaults are carried out by acquaintances, romantic partners and friends. The cute freshman living down the hall in residence, who, after a night of too much drinking and some mutual fumbling, pushes a little too hard, past an awkward "No." Or that sweet friend you've been hooking up with, who, one afternoon in a dorm room, forgets to make sure you're still on board. You give in. He thinks it's okay. "It was so grey," you say later. "It was so complicated."

It's not politically correct to say that consent is complicated, yet here we are, 50 years after the dawn of second-wave feminism, still struggling as a society to define it. Consent gets muddled up in gender roles; in the depressingly retro narrative that men chase, while women are coyly chaste; and in enduring misogynistic slang in which a one-night stand is called a "fuck it and chuck it" and guys tally their sexual partners by "kill counts." It's fogged up even more by alcohol in a world where binge drinking is practically a required first-year course in the minds of many coeds. We need to find a solution: for victims, of course – but also to empower both men and women, straight and gay, to make sex safer in a sexually permissive society. For that to happen, consent can no longer be something given up, or offered up, with one gender (i.e. mainly women) expected to guard chastity's gate.

"These are situations with huge consequences, and you're just trying to figure it out," says Garret LaValley, 22, a business student at the University of British Columbia, recalling his own sudden immersion in the party culture on campus three years ago. "It's a weird, steep learning curve."

As a varsity athlete, Mr. LaValley says the pressure to score was heavy, especially as a freshman among older, more experienced teammates. He remembers getting drunk and making out with women on the dance floor, wondering what should come next. "Do you just immediately take them home? How will people react if I do or don't? What do people expect?"

That's a complex question, especially in an era of mobile apps like Tinder, and in the gay community, Grindr, which are elbowing old-fashioned date culture aside as they allow people to search out hookup options in their immediate geographic vicinity: Having a Tinder profile, in the words of one student, suggests consent has already been given. One attempt to clarify consent via technology was the Good2Go app, launched last spring, which asked both parties in a potential hookup to record their level of willingness to have sex, as well as how drunk they were; the results were then sent to their respective e-mail accounts. The app was roundly criticized for potentially providing a fabricated defence against sexual-assault allegations, and last month Apple yanked it from iTunes.

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Believing that issues around consent can be solved by checking off a box on a mobile app – or even, frankly, by devising a snappy slogan – suggests that what's at issue is merely a problem of miscommunication. But human beings can read body language in the bedroom as easily as they can in other social interactions, argues Melanie Beres, a senior lecturer at the University of Otago in New Zealand, who has researched consent in Canada. "Women say 'No' to sex in the same way everyone declines all kinds of social interactions, and men are quite adept at hearing those refusals as refusals," says Dr. Beres. "[Sexual assault] is about someone making a decision to ignore the cues." (This appears to include the "cue" of being incapacitated: A forthcoming University of Windsor study conducted on three Canadian campuses found that 79 per cent of rape victims said they "were too drunk or out of it to stop what was happening.")

What's promising about Yes Means Yes is its potential to change the communication around sex. "Do we want to talk about just avoiding criminal activity?" asks Dr. Bere. "Consent is also about making a dividing line between okay and not-okay sex, and we don't want to aim for sex that is just over the line." Yes Means Yes, in other words, might be an important step toward creating healthier, more open conversations about sex – a worthy and overdue goal, to be sure. But it isn't necessarily a strategy for reducing assaults.

Law and ethics

In late October, the Massachusetts Institute of Technology released a student survey in which 15 per cent of women and 5 per cent of men reported experiencing sexual assault – with such assault defined as unwanted contact, from touching to penetration, that involved force or threats of incapacitation – while attending the school. Even more troubling was how students responded to and perceived those assaults. Of the victims, 72 per cent said they didn't think it was "serious enough to officially report," and 44 per cent said they felt "at least partly responsible" for what had happened. Overall, one-quarter of men and 15 per cent of women agreed that a drunk person who is assaulted is "at least somewhat responsible," and more than half of all students agreed that "rape and sexual assault can happen unintentionally, especially if alcohol is involved."

That's a disturbing finding: If rape can happen "accidentally" between drunk students, then who's to blame? Not the guy, it seems: Roughly one-third of the students surveyed agreed that rape happens "because men can get carried away in sexual situations once they've started." In other words, many of today's educated millennials – a generation idealized for its egalitarian values – still believe that men "can't help it," and that drunk women who cross their paths have themselves to blame. Changing those attitudes will doubtless take more than Yes Means Yes banners and campus bar coasters.

Consider that friends-with-benefits scenario at McGill. Did it constitute sexual assault? The woman says no, it did not: Yes, she was drunk, she acknowledges, but so was he. And she points out that they knew each other well, that they had done it before, and that she hadn't really protested – and if she had, she hastens to add, without doubt he would have stopped. Still, she concedes, the lines feel blurry. "I find it really hard to define sexual assault when it involved me." And then this, which seems hardly to clarify matters: "I should be able to define my experience as I choose."

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This is an example, says Dr. Beres, where it is unproductive to focus on drawing a legal line without considering ethics. "Consent is too low a bar," she says. Even if what happened in that dorm room didn't meet the criminal definition of sexual assault, it was sex that the woman didn't want. It was sex that wasn't fun.

This focus on legality – on what constitutes crossing the line – was an ongoing theme in my interviews with students. They could easily define sexual assault in stereotypical situations: a surprise attack by a stranger; a man who threatens or physically forces a woman; a sober person who forces sex on someone who is stumbling drunk. And the men I spoke to unanimously agreed that responsibility to get consent fell more heavily on them: "Just by how we are made, the onus should be on the guy," says Mr. LaValley. "He is in a situation where he can take advantage of somebody."

In Canada, consent requires taking "reasonable steps" to ensure it exists. Being drunk is not a defence for failing to get consent, and neither is arguing that consent was given in advance. As one recent campus campaign put it: "If it's not loud and clear, it's not consent." A meek okay and half-hearted "Yes" doesn't count.

But the law doesn't clarify every question. Students also wonder, in the words of Mr. LaValley, "If you had sexual experiences with the same person, and it's common knowledge that you would hook up if you were drunk," is that still breaking the law? How drunk is too drunk? What if the woman – or as one female student pointed out, the guy – didn't really want to, but gave in? What if the initiator genuinely thought he or she had consent? This is where a discussion around the ethics of sex – rather than simply what counts as a crime – ay prove more productive in the long run.

Morning-after uncertainty

One of the problems with the new campus campaigns, whose champions have worked to convince students that "consent is sexy" (in an echo of the AIDS-fighting promotion of condoms) is that the new consent instruction manual is about as sexy as a cold shower. Demanding an unequivocal verbal "yes" – not just once, but at every step along the way, from kissing to intercourse? Get real. Who's going to do that? Hot sex, as portrayed on television or in the movies – let alone in ubiquitous Internet porn – looks nothing like that. A recent poker-faced American sexual-assault campaign depicted what enthusiastic consent would look like with a cheesy YouTube video in which a male pizza deliverer and the woman who answers the door have sex, all the time breathlessly murmuring to each other, "Is this okay?" It played like a skit on Saturday Night Live.

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For many students, requiring verbal consent goes too far, says Daniel Smeenk, 22, recently graduated from the University of Toronto. While the initiator has to stop if consent isn't clear, Mr. Smeenk argues, "the person who doesn't want to consent should be very clear that they don't. Sexual encounters aren't like signing a contract. It's not like you simply lay down the conditions, ask them to sign here, and then go forward. There's a lot of romance. There's an almost inexplicable human intimacy involved. Some of it might be cultural, some it might be just simply how we're wired, but there's a large part of us [that] wants things to be spontaneous and free – and it enhances our experience."

When verbal consent is raised at workshops in residence at McGill, where they have been mandatory since 2005, student leaders say participants often argue that body language should be enough – that asking permission is "awkward," in that it suggests the guy, still usually expected to initiate sex, "doesn't have game." Peer facilitator Sarah Southey, for instance, says at one particularly vitriolic session in September a male student asked, "What happens if she is a virgin and doesn't know she wants it?" Says Ms. Southey, "That was very rattling. As if he was saying, 'She wouldn't actually know what she wants, and I know it better.'"

It's not only men who struggle with such boundary lines. "I think you consent when your hand goes down or your bra straps come off," says Alex, 19, a female second-year science student at the University of Toronto. "If you start talking, it almost breaks the moment, it takes away from the natural flow of it." She understands why guys would be reluctant to ask for consent out loud: "A verbal rejection is much harsher than moving away a hand."

A harsh rejection, however, is infinitely preferable to a sexual assault. While no one I spoke with admitted to forcing a partner intentionally, several male university students acknowledged feeling a morning-after uncertainty about whether their partner had been into it, and wondered if they had crossed the line. Setting the bar at verbal consent is meant to remove most of that doubt. And, suggests Dr. Bere, pivoting the discussion away from No Means No, and toward sexual education that focuses on ensuring both partners are willing and enthusiastic, is an important step forward.

Seen in that light, affirmative consent could be a powerful tool to make sex better, allowing individuals to define what they want – and to clarify what that looks like to their partners. Saying 'Yes' is empowering, explains Madeline Hancock, a University of Toronto student. "It's also a recognition of the idea that any sexual activity should not be a competition, but should be co-operative: for the mutual benefit of both partners."

Sex, in other words, shouldn't be about trying to make sure your partner doesn't say no. "The point of the game," says Ms. Hancock, "is that everyone involved really wants to be doing it."

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Enduring double standards

All of which introduces another question: Why do we wait until teenagers have arrived at university, and are in the middle of the most exciting, jam-packed and sleep-deprived week of their lives, before we seriously educate them about consent? According to Scott Anderson, a UBC researcher who studies consent, it all goes back to how conflicted society is about granting young people – especially young women – the permission to have sex at all. "They have enough information to know that birth control is important," he says, "but other aspects are much less clearly explained, because there is still a hesitation to say, 'Sex is okay.' "

U of T student Alex puts it this way: "Parents influence this culture of casual sex [being] slutty for girls, but an achievement for guys. A lot of my guy friends are always encouraged to be sexually active by their father, but girls' fathers are so against them having sex. This leads to girls being very quiet about their sex lives." In Alex's case, her father's sex talk amounted to being handed the same book he'd been given as a youth in Sunday school, which was "basically all about abstinence."

Entwined with that is a message to young men that sex is a conquest that they are expected to win, says Joe Maguire, a sexual-assault educator who runs a program for men at the University of Calgary. "If you are being pressured to have sex a lot, then you are not really going to be looking for consent," he says. "You're just trying to get laid."

Not, of course, that it's black-and-white. Alex admits to flirting aggressively with a young man at a club, even though she "could tell the guy wasn't into it." They kissed, and it stopped there, she says. "But afterward, I thought, 'How would I feel if a guy had done that to me?' "

That gender dynamic is also complicated in sexual encounters between LGBT women and men, even though their voices have often been missing from consent campaigns. "As a single gay male, the expectation is that [you're] always ready for it," says Mac Chapin, 20, a third-year international-relations student at the University of Toronto. "For men, there is never a question of 'yes means yes,' because 'yes' is always assumed to be the answer."

In the straight world, meanwhile, the cultural bias that woman should resist sex – that they don't have an equal responsibility to make the choice – is one the female students I spoke with summarily rejected. Last year, Alex says, she was making out with a guy she had just met when he asked if she wanted to go further. She said no, and, she recalls, "He was so respectful and okay with it, and I've never felt that empowerment before. Honestly, it was the first time, I was like, 'No, I don't want to do this,' and my decision was so respected." Usually, she says, men act like "No means try harder."

That's why Yes Means Yes is such a powerful idea, Alex says. It removes the "No-means-try-harder" that stems from traditional expectations. "I am quite explicit when I want to have sex, and I try to avoid playing games at all costs," she says. "If you are very clear about what you want, then if you do say 'No,' it resonates more."

Among those men interviewed for this story, it was the older ones who most fully backed the spirit of Yes Means Yes. That includes the male half of that unfortunate, liquor-infused incident at McGill. Months after that day in residence, when they finally discussed what had happened, and the female student shared her side, he had been horrified to learn she wasn't an enthusiastic participant. He told me that it's irrelevant to him whether what happened met the legal definition of assault. "I interpreted there to be more comfort than there was," he says. "I know it would have been a lot better to check in." Looking back on his early experiences with sex, "there are so many things I was doing wrong, so many poor decisions."

Now, he adds, he always asks for verbal consent – at every step of sex, from kissing to intercourse. "Consent is sexy," he says. "It shows you care. There's nothing better than when you know you have full permission."

When it comes to humanity's most intimate act, isn't that where the conversation should start?

With reports from Iris Robin and Davide Mastracci.