IT'S not a sophisticated message and yet it appears to need repeating: sex without consent is rape.

Sir Stephen House, the chief constable, reiterated this statement on Wednesday at the launch of the latest phase of Police Scotland's rape prevention campaign, We Can Stop It.

Aimed at 16- to 27-year-old men, who are responsible for more than one third of reported rapes in Scotland, We Can Stop It is a perpetrator-focused approach that, in this phase, aims to make clear the definition of rape and also looks to train bar staff in intervention methods.

There is a dual message to be understood here: that everyone in a community is responsible for helping to prevent sexual assaults and that the definition of rape is unequivocal.

The bystander approach is becoming more common as a tool to tackle sexual violence, particularly in the night-time economy where alcohol can be used as a weapon to make women vulnerable.

The Green Dot programme in the US is used to promote the idea that green dots represent bystanders to violent sexual behaviour who should be motivated to something - anything - to divert disaster. The scheme works on the premise that everyone in the community has a responsibility to take action if they see something happening.

Similarly, last year President Barack Obama launched part of a university sexual assault reform campaign: a project aimed at men on campus called It's On Us, encouraging them to intervene. It challenges students on university campuses to see sexual violence as their individual responsibility to prevent.

Prevention, however, doesn't have to start at the point of crisis; it's possible to be active in attempting to prevent sexual violence by challenging the insidious attitudes that allow attacks to happen.

There is a need for men to talk among themselves. To have conversations about what's ok and what is emphatically not.

When their friends make rape jokes, or sexist comments or catcall at women in the street - to simply and politely shut that stuff down. When inappropriate comments are made on Facebook, to challenge them. To not be that guy.

When their friend is preying on the tipsy girl in the nightclub because she's an obvious, easy target to secure Sunday morning's bragging rights, have a word.

To understand that any failure to challenge negative attitudes is to help normalise the view that there are blurred lines or grey areas where predatory behaviours are alright.

Let's remember, the majority of men know all this already, they're clear on right and wrong. They don't need the President of the United States to point it out to them, they don't need Scotland's most senior police officer. Some, a rank few, need everyone to point it out.

Just as valuable as telling men not to rape is telling young men - and young women - about the notion of enthusiastic consent. That it's not just important to not hear a no but is vital to hear a clear and repeated yes, that coerced consent is not consent. To shift the emphasis from "no means no" to "yes means yes".

How simple it seems to make the point that men should only have sex with conscious and enthusiastic partners; how simple to any right-thinking person does it seem that men should only want to have sex with conscious and enthusiastic partners.

Affirmative consent is already written into law in California but it seems a rarely heard of concept in the UK. For rape prevention tactics to be successful in Scotland, it should be part of the conversation with young people who are making their first explorations into the complicated, convoluted world of romantic relationships.

It takes a degree of bravery to step up and step forward when a woman, a stranger, is at risk. It also takes a degree of bravery to have these conversations.

But to prevent sexual assault by telling young men to gain consent, we need to start having frank conversations about the nature of consent and what that means.