The first-year law students I teach – smart, insightful, idealistic – have come of age hearing that "no means no" when it comes to sex. They are almost always stunned to learn that, in most states, the legal definition of rape still requires the use of physical force. In other words, a verbal "no" isn't always enough.

Such reactions underscore the extent to which the law lags behind a widespread belief that intercourse without consent is rape, and it should be punished accordingly. Indeed, while non-stranger rape is by far the most common rape scenario, with an estimated nine out of 10 women knowing their assailant, the criminal law was not designed to punish it. Most rapes by intimates and acquaintances are never prosecuted, or even brought to the attention of the police, contributing to their relative absence in mainstream media.

The good news is we've arrived at an opportune moment for change. For the first time in more than 50 years, the rape statute offered as a model for state legislatures and courts – the so-called Model Penal Code – is under revision by the American Law Institute (ALI), an influential body of judges, practitioners, and legal scholars dedicated to improving the law. When the American Law Institute speaks, state legislatures tend to listen. A better model rape statute will likely lead to better rape laws – and ultimately more convictions.

First of all, the ALI needs to remove the force requirement that still exists in just over half the states and the Model Penal Code. That's because, unlike sexual assaults by the archetypal knife-wielding sexual predator, acquaintance rape cases often involve little, if any, force. For that reason, in most jurisdictions, such cases may not satisfy state law definitions of rape, regardless of how clearly the woman said "no".

Consider the notorious case of Steubenville, where a naked victim was penetrated while she was passed-out drunk. In a text message admitted in evidence, one of the two defendants described the teenager as "like a dead body". Most would agree that the girl was raped because she did not consent to the sexual conduct.

But rape law is more equivocal. In Ohio, as in most states, rape is not non-consensual sex. Instead, it is sexual conduct "when the offender purposely compels the other person to submit by force or threat of force". The use of force makes non-consensual sex rape; non-consent does not.

Related to the force requirement is the law's traditional insistence that a woman could not be raped if she did not resist her rapist. Although this obligation has been softened or eliminated, depending on the jurisdiction, a woman's resistance remains a marker of whether enough force was used for sex to count as rape. This reality can explain the provision used to prosecute the Steubenville defendants: it is a crime to engage in sexual conduct with a person whose "ability to resist or consent is substantially impaired because of a mental or physical condition". In other words, the young men were not convicted because the victim did not consent; they were convicted because she could not consent.

Because prosecutors had evidence that this young woman was passed out at the time she was penetrated, the case for rape was an easy one. She could not resist, and she could not consent. Had she been less drunk, though, the prosecution would have had a far tougher time of it. The woman's non-consent, even if the jury believed her, would not have been enough to prove rape.

Removing the force requirement is a crucial first step as the ALI proceeds with its revisions. Equally important is the development of a workable definition of consent that aligns with contemporary sexual norms. An affirmative consent standard can clarify the outcome of cases that recur with depressing frequency – cases where passivity results from extreme intoxication, often to the point of unconsciousness.

A handful of states adopt this approach, rightly demanding some demonstrated intent to have sex. One good example is Minnesota's statute, which requires "words or overt actions by a person indicating a freely given present agreement to perform a particular sexual act with the actor". What's more, the statute emphasizes that "consent does not mean the existence of a prior or current social relationship between the actor and the complainant or that the complainant failed to resist a particular sexual act". Under this framework, lawful sex must manifest a real choice. Sex with someone who is "like a dead body" does not qualify.

Today's rape law is in desperate need of modernization, and current efforts to reform the model statute can lead the way. Non-stranger rape should not elude justice.