As far as legality is concerned, you need two key things to be able to give consent: Knowledge of what you’re consenting to, and then the actual consent.

The second part is very straightforward, so I’ll touch on that first. Because if someone is unconscious, they obviously can’t consent. It’s an easy argument to satisfy; If they didn’t/couldn’t say it was okay, then it wasn’t okay. Easy. They were passed out? Then they couldn’t consent.

The big reason it can get murky is because that communication can happen nonverbally, via body language and context. Maybe someone misinterprets a signal, and goes in for a kiss that the other person doesn’t want. That’s a tame example, but it gets the point across with how the actual communication could get murky. But again, this is certainly the most straightforward part of consent. Can they say yes? Did they say yes? Cool.

The tricky part is that first one: Knowledge of what they’re consenting to. It gets tricky because the line gets blurry when alcohol is involved. The most straightforward times this gets violated are when one partner is surprised by something. “Stealthing” (taking a condom off without the other person’s knowledge) is rape because it violates this first part of consent. They weren’t given sufficient knowledge of what they were consenting to, (because they believed their partner was wearing a condom) so it isn’t consensual. Everyone involved needs to be able to comprehend what is happening when it’s happening. You can be blackout drunk but still able to understand what is happening in the moment. Being blackout just means the “record” part of your brain was turned off. But you can still be awake and aware of your surroundings, even if you won’t remember any of it once you sober up.

This is why lots of rape cases get thrown out. The victim was enthusiastically consenting at the time, but doesn’t remember it because they were blacked out. They wake up the next morning and are horrified about what they participated in. If they were blackout, they may not even remember consenting at all. But if they were capable of understanding things at the time that it was happening then the first part is still (as far as the law is concerned) satisfied. The law doesn’t care if you regret it after the fact, or if you can’t remember consenting, or if you only consented because your inhibitions were lowered and you had beer goggles on. All the accused rapist has to do is prove that you were able to understand what was happening, (or at least convince the jury that you were) and that you went along with it with that knowledge. If they’re able to do that, (and if the jury isn’t biased) then they’ll be acquitted. Because as far as the law is concerned, if those two parts of consent are fulfilled, then you were able to consent.

The courts do take a lot of factors into consideration, but generally speaking, voluntary intoxication has a high threshold to meet. The victim usually needs to be passed out (or at least so drunk that they’re not capable of communicating their consent). Because the courts will go “well they knew what they were doing until they passed out, because they knew they were intoxicated.” Involuntary intoxication (like having a drink spiked) is typically a much much lower threshold. If a victim was drugged, they’ll have a much easier time proving non-consent, because courts will tend to go “well they didn’t intend to get intoxicated, so any consent they gave while intoxicated should be considered coerced.”