Arbitrary lines and the age of consent

Laws sometimes impose restrictions by way of categorical lines. For example, in the UK, you can’t vote unless you’re 18, legally drive or drink before you’re 18, nor have (legally) consensual sex before the age of 16. One common complaint against these types of restrictions is that the lines in question are arbitrary. I will argue that at least some of these complaints are philosophically confused, and make my point with reference to the age of consent.

The relevant confusion can be illustrated with reference to a recent episode of the Guardian’sPolitics Weekly. The host, Tom Clark, brings up a 1979 Home Office report on the age of consent recently obtained by the Guardian, and says: ‘not everything that they were saying was ridiculous, they were saying maybe the age of consent is an arbitrary line’. Edmund Fawcett chimes in by saying ‘well, it has to be an arbitrary line’, and Clark agrees.

Before saying what’s mistaken about this exchange, let me say what I think is going on here. The review is pointing to reasons for lowering the age of consent. Clark seems to think that at least some of these reasons are not without merit, and also seems to think that this entails that the current line at 16 is arbitrary. Why is he saying that? The reason, I think, is that he’s relying on the following premise:

(P) If there is some number n such that we could have imposed an age of consent limit at agex +/-n with good reason, then imposing a limit at age x is arbitrary.

After all, if we assume (P), we can make sense of what Clark is saying: If, as Clark suggests, the Home Office report suggests some good reason for an age of consent different from one at 16, then it follows from (P) that:

(C) Our current age of consent limit at 16 years of age is arbitrary.

But (C) is false. The reason that Clark ends up with (C), is because of (P), and that gets to what I think is his mistake: (P) is false. Moreover, I think that what leads him to (implicitly) appeal to (P) is a confusion between arbitrary limits and what I will call non-uniquely warranted limits. Let me explain:

Arbitrary limits are limits that we have no reason to impose. For example, a law that said that everyone whose last name starts with the letter ‘a’ through ‘m’ are able to legally consent to sex, and that no one else is, would be arbitrary. We have no reason to think that facts about last names track morally relevant facts about consent, which is why we lack reason to impose that particular limit.

Notice, however, that that’s not the situation we’re in with our current age of consent. I take it that we have good reason to believe that most 16 year-olds are competent to make the relevant decisions, and that lots of people younger than 16 are not. That give us good reason to go with an age of consent at 16. That’s also why it’s not an arbitrary limit, as ‘arbitrary limits’ were defined a moment ago.

But, Clark might say, what about 15? Maybe it’s also the case that most 15 year olds are competent to make the relevant decisions, and that lots of people under the age of 15 are not (the latter would follow from what we’ve already said about lots of people younger than 16 not being competent). In fact, for the sake of argument, let’s assume that that’s the case. Still, it doesn’t follow that an age of consent at 16 is arbitrary, contrary to (P). To see why, consider an analogy:

The speed limit in built-up areas in the UK is 30 mph. Arguably, we have good reason to impose a limit at 30, since doing so saves lives. But why not impose a limit at 35? Let’s assume that all the reasons that speak for 30 also speak for 35, and that there are no sufficiently strong reasons against either. That means that both limits are warranted, but that neither is uniquely so. That is, they’re both non-uniquely warranted limits. We may go with either limit but can’t impose both, so go with one of them.

The assumption just made about there being equally good reason for either limit might be false, of course: maybe we have better reason to go with 30 than with 35, on the grounds that a limit at 30 makes for a better trade-off between convenience and number of casualties. And similarly for our age of consent: maybe we have better reason for going with 16 than with 15, on the grounds that an age of consent at 16 makes for a better trade-off between forbidding competent people from having sex and allowing non-competent people from having sex than does a limit at 15.

But notice that that’s a different issue from the one relevant here. The exchange between Clark and Fawcett is not concerned with which one of two (or more) good limits on the age of consent should be imposed. As I’ve reconstructed the exchange, it’s concerned with whether the very fact of there being two (or more) good limits on age of consent makes picking either arbitrary. I’ve suggested that it doesn’t, and that Clark’s mistake of thinking that it does owes to him confusing arbitrary limits with non-uniquely warranted limits, and thereby accepting something like (P).

So, in conclusion, we shouldn’t confuse limits that we lack reason to impose (arbitrary limits) with limits that are not unique in being such that we have reason to impose them (non-uniquely warranted limits). This applies to the other limits I mentioned at the outset as well: age restrictions on voting, driving and drinking. In these cases, too, we shouldn’t make the mistake of thinking that any reasons uncovered for imposing a different limit entail that our current limit is arbitrary.