The first line in the feminist battle against male violence isn’t always “I believe her”. Sometimes, she is not to be believed. The BBC Two documentary Police Under Pressure: Sex Crime, broadcast last month, followed South Yorkshire Police through two investigations into missing teenage girls. They receive a tip-off that one girl has been seen at a hotel in Bradford, and we watch Detective Constable Karen Cocker watching the CCTV. What she sees is unmistakable. The girl scampers down the staircase after a man, squirming against him giddily. “She dunt look like she’s there reluctantly. She looks like she’s there because she wants to be there, dunt she?” says a male hotel employee, sounding almost hopeful that this apparent enthusiasm will prove . . . something. “I think we’ve got to bear in mind her age,” says Cocker, soft but terse. “She’s 13.”

Further footage shows that there are three men with the girl. They lead her in and out of different bedrooms. It is a record of pimping and raping in progress. But when the officers catch up with the girl, she denies that any crime has taken place: she was there willingly, she says, and none of the men had sex with her. Cocker does not believe her. Physical evidence supports what the video suggests: the girl has been raped, by so many men that it is impossible to identify any individual’s DNA from the sample. Victims tell these kinds of lies all the time. They lie because they are afraid of the police, or because they are afraid of the perpetrators, or they lie to themselves, because they are afraid of knowing they have no control. They lie by retelling the lies that they have been told by the men who abuse them: he loves me, he’s my boyfriend, he said I wanted it really.

“I believe her” is powerful because it’s simple; because it’s simple, it slides into being simplistic. This is the way of effective slogans, and I am not going to reject it for being effective. We know that “he said, she said” is not an equal equation. Habit and tradition mean that what he says is heard, while what she says must scale mountains of reflexive doubt before it even registers as a whisper. “I believe her” is a promise, simply, that we will listen – that, over the hum and throb of the misogyny that we live in and that lives in us, we will let her voice reach us. In a crude sense, this is just a matter of playing the odds. We know that male violence against women, including sexual violence, is endemic. When a woman tells us a man has harmed her, the probabilities are standing on her side, if we are willing to acknowledge them. (Not everyone is, of course.)

But “I believe her” is a beginning, and not an end. In the post-mortems of Rolling Stone’s A Rape on Campus story, a lot of scrutiny has fallen on “I believe her”: the failure of journalist Sabrina Rubin Erdely to appropriately factcheck the account of a gang rape given by her source Jackie is counted as a failure of excessive belief. The first version of Rolling Stone’s retraction (now edited) read: “our trust in [Jackie] was misplaced”. There’s something sickly about this insistence that the publication’s only vice was too much virtue. In reality, there is plenty that Erdely and her editors could – and should – have checked in the process of putting together the story, and none of these checks would have implied cynicism about Jackie as a victim. Details such as the date of the party at which she was assaulted, and whether the boy she alleges took her to the party was a member of the fraternity she named, have been shown to be uncertain after publication. Rolling Stone had a duty to its source to check those details before.

Those inaccuracies might have been of no matter to the overall narrative. Rape is traumatic, memory is uncertain, and after two years, maybe these are understandable lapses. (I got flashed once. The police came to my house immediately with mugshots of likely offenders, which I dutifully flicked through while I became gradually aware that my brain in its shock had stored nothing but a blur of hideously pink penis poking from some green cords, then completed the picture with the face of an outdoorsy TV presenter who definitely wouldn’t have been hanging around in a Sheffield underpass. Brains are strange. They often let us down.) But, understandable as they might be, they should not have appeared in the published version. If Jackie’s story proved impossible to reconcile with the facts, it shouldn’t have been published at all. Certainly, it makes no sense at all to me that Rolling Stone would agree not to present Jackie’s claims to her alleged attackers because she feared reprisals – but then use her real first name in a story which gave sufficient detail to make her exposure inevitable.

In this instance, “believing the victim” seems to have been nothing but a dereliction of moral duty on the part of the publication. It is right to accept every testimony of victimhood in good faith, and it is right for police and journalists to test that faith with a confirmation of the available facts. We don’t know what happened to Jackie: even if she committed outright fabrications (something far from proven), that does not not mean her testimony of rape is false. All kinds of women become victims of sexual violence, including ones who are otherwise liars. But by publishing this young woman’s story without checks or anonymity, Rolling Stone has left her open to an incredible volume of abuse – a young woman who, even according to her most sceptical friends, showed every sign of having experienced some kind of profound trauma in September 2012. (You may notice that I am not particularly concerned about the effects of this flawed reporting on the alleged perpetrators. That is because there haven’t really been any: feminists didn’t dox any fraternity members. Only the alleged victim has had her name and address broadcast, along with public calls for her to be punished. Unpleasant as this is for the young men who appear to have been wrongly implicated, they will recover, and Jackie may not.)

The belief we extend to victims is not unconditional. We believe because of what we know: about violence in general, and about the specifics of the case. So what about when the person we are asked to believe is not a her? Shia LaBeouf claimed to have been “raped” by a woman while he took part in an art installation, and several feminist writers have suggested that there is a “feminist imperative” to believe him, as we should believe all victims. But there is a serious problem here: it is very hard to know what LaBeouf is asking us to believe. Rape, generally understood as forcible penetration with a penis or other object (not least under English law), could not have taken place in this instance, and LaBeouf does not specify what did happen. There is no form of sexual violence committed by women as a class against men as a class, and there is no extended cultural history of disbelieving men in any case: “believing him” simply means granting the default authority to male words, in a situation where it is impossible to know what they signify. If “I believe her” has become totally detached from the analysis of male violence and female oppression, then it has also become meaningless.

In Police Under Pressure, several of the abusers of the girl at the hotel are convicted – largely thanks to physical evidence. The second girl is found at the home of a man in Bradford. Again, she initially denies that any sexual activity has taken place, but after careful interviewing, she is willing to testify. A case is put together and brought to court. But the girl is found to have made a false statement under oath about a matter not related to the substance of the case. She is not believed. The man in whose home she was found goes free. It is a wrenching thing to watch this injustice take place, and all the more so because it is normal: just a little over 1% of all rapes will result in a conviction. Most rapists walk, and often they walk simply because women’s words are not considered strong enough to stand in court. This is why “I believe her” matters. It is not the cheat answer to difficult questions of fact. It does not exonerate institutions from their other duties to victims. It is not a shortcut to justice. It is just the start when we look for the truth about male violence. We still have the rest of the work to do.