In September, 2014, Governor Jerry Brown signed Senate Bill 967 in to law, requiring colleges in California to adopt certain policies dealing with campus sexual assault in order to maintain their eligibility for state funding. One of the most controversial requirements of the bill was a mandate that campuses adopt a policy of “affirmative consent” for sexual activity.

According to the law,

“Affirmative consent” means affirmative, conscious, and voluntary agreement to engage in sexual activity. It is the responsibility of each person involved in the sexual activity to ensure that he or she has the affirmative consent of the other or others to engage in the sexual activity. Lack of protest or resistance does not mean consent, nor does silence mean consent. Affirmative consent must be ongoing throughout a sexual activity and can be revoked at any time. The existence of a dating relationship between the persons involved, or the fact of past sexual relations between them, should never by itself be assumed to be an indicator of consent.

Some commentators, such as Reason’s Cathy Young and George Mason law professor David Bernstein, have criticized the law’s requirements as overly demanding, and a symptom of “moral panic” over campus hookup culture.

But there’s certainly nothing objectionable in the idea that consent ought to be consensual. And there are good reasons for thinking that a policy of “affirmative consent” is an improvement over previous understandings of what genuine consent requires.

Consider the old slogan of those opposed to sexual assault: “no means no.” So far as it goes, this is a true and important principle of sexual morality. If a woman says “no” to a proposed sexual encounter, then that should be taken as a denial of consent, not as a challenge to the man to ramp up his seductive “game.” If a man continues to kiss, undress, or touch a woman who has said “no,” he is morally guilty of sexual assault, whether or not he has used physical violence to subdue her, and whether or not she has used physical force to resist him.

But even if “no means no,” this clearly does not entail that the absence of a “no” means “yes.” To see this, consider the following cases:

Intoxicated: After consuming a significant amount of alcohol in A’s presence, B passes out on the couch. A then undresses B and has sexual intercourse with her. Afraid: A and B meet in a bar and go back to A’s apartment. B rebuffs A’s advances. A smiles at B and says, “Look, you’re alone with someone you don’t know, who’s much bigger and stronger, and, for all you know, has beaten and raped several women. Maybe I’m not as nice as I seem.” B is very frightened by A’s remarks and does not resist A’s advances.* Incapable: B is a 19 year-old woman suffering from a severe intellectual disability, with an IQ of 59. A is aware of B’s condition, and begins to play a “touching game” with B, involving mutual undressing and touching of genital areas. B engages in this activity without protest.

In none of these three cases does B say “no.” But neither does B give valid consent. In Intoxicated, B is completely unconscious and unaware of what A is doing. In Afraid, B has a reasonable fear that A will use physical violence against her if she does not go along with his demands, and in Incapable, B lacks the mental capacity to give valid consent to sexual relations in just the same way that a child does. In all three cases, then, A engages in sexual activity without B’s valid consent, and is morally (and probably legally) guilty of sexual assault.

It was consideration of cases like this that led many reformers to conclude that “no means no” was inadequate – not wrong, exactly, but not the whole truth, either. Consensual sex requires more than just the absence of a “no.” So, rather than a policy based on “no means no,” these reformers thought, we need a policy of “yes means yes.”

But this is where things started to go wrong. For some people drew the conclusion that the problem with cases like Intoxicated – an all-too common occurrence on college campuses – was that B never gave explicit consent. Thus, the Office of Violence Against Women, a subsidiary of the US Department of Justice, writes on its website that “[s]exual assault is any type of sexual contact or behavior that occurs without the explicit consent of the recipient” (emphasis added). And some reputable organizations and individuals have interpreted California and New York’s affirmative consent policies as enacting a similar requirement.

But if “affirmative consent” policies are interpreted as requiring explicit consent, and indeed as requiring that such consent be “ongoing throughout a sexual activity,” then those laws really would be, as some critics have charged, indefensible. Should a couple who has been dating for two years and who have had sexual intercourse hundreds of times really be required to obtain explicit verbal consent before each and every sexual encounter? Should they be required – like students were under the justly ridiculed Antioch college policy – to obtain a new statement of consent for “each new level of sexual activity,” with the stipulation that “body movements and non-verbal responses such as moans are not consent”?

The answer to both questions is obviously “no.” Genuine consent is vitally important, and there really is a serious problem of sexual assault on college campuses, mostly stemming from the prevalent use and abuse of alcohol. But we can admit that consent is crucial without concluding that consent has to be explicit.

Properly understood, “affirmative consent” means that a person has engaged in some form of outward behavior that would lead a reasonable person to conclude that she is an active and voluntary participant in sexual activity. That behavior could take the form of saying the words “Yes, I would like you to have sex with me.” But that’s obviously not the only form it could take. Valid consent can be implicit as well.

What counts a valid token of implicit consent will vary from context to context. Still, it is reasonable to suppose that in most circumstances, B’s pulling A into bed and undressing him would count, as would B’s smiling, moaning, and kissing A in response to A’s undressing and caressing her. A lot will depend on the history between A and B (although California law is certainly correct to state that a prior history of sexual activity is not sufficient to constitute consent), their reasonable expectations, and the particular nonverbal cues they use to communicate. But even if it can be hard for an outsider to correctly interpret such subtleties, surely no one with any experience of intimacy would doubt that this kind of nonverbal communication and consent is not only real, but totally commonplace.

Thankfully, as Slate’s Amanda Hess noted, nothing in California’s law can reasonably be read as requiring explicit consent. Indeed, in the process of crafting the law, legislators actually deleted from the bill language that warned that “relying solely on nonverbal communication can lead to misunderstanding,” indicating that they wanted to allow room for ordinary, implicit consent.

Anyone concerned with the rights, dignity, and physical and emotional well-being of college students should regard policies that insist upon the consensual nature of sexual activity as vitally important. And while laws like California’s that require “affirmative consent” can – and have – been misinterpreted in ways that undermine rather than promote individual autonomy, both the philosophical foundation and the text of those laws are sound.

* I borrow this example from Alan Wertheimer’s excellent book, Consent to Sexual Relations, and highly recommend that work to anyone interested in diving deeper into the legal and philosophical issues surrounding this fascinating and important topic.