A new arrival, Kouran, recently challenged our conventional use of the label "rational" to describe various systems. The full thread is here, and it doesn't summarize neatly, but he observes that we often use "rational" in the context of non-intellectual, non-cognitive, etc. systems, and that this is an unconventional use of the word.
Unsurprisingly, this led to Standard Conversation Number 12 about how we don't really use "rational" to mean what the rest of the world means by it, and about instrumental rationality, and etc. and etc. In the course of that discussion I made the observation a couple of times (here and here) that we could probably substitute some form of "optimal" for "rational" wherever it appears without losing any information.
Of course, status quo bias being what it is, I promptly added that we wouldn't actually want to do that, because, y'know, it would be work and involve changing stuff.
But the more I think about it, the more it seems like I ought to endorse that lexical shift. We do spend a not-inconsiderable amount of time and attention on alleviating undesirable side-effects of the word 'rational,' such as the Spock effect, and our occasional annoying tendency to talk about the 'rational' choice of shoe-polish when we really mean the optimal choice, and our occasional tendency to tie ourselves in knots around "rationalists should win". (That optimized systems do better than non-optimized systems is pretty much the definition of "optimized," after all. If we say that rational systems generally do better than irrational systems, we're saying that rational systems are generally optimal, which is a non-empty statement. But if we define "rational" to mean the thing that wins, which we sometimes do, it seems simpler to talk about optimized systems in the first place.)
There's precedent for this... a while ago I started getting out of the habit of talking about "artificial intelligences" when I really wanted to talk about superhuman optimizing systems instead, and I continue to endorse that change. So, I'm going to stop using "rational" when I actually mean optimal. I encourage others to do so as well. (Or, conversely, to tell me why I shouldn't.)
This should go without saying, but in case it doesn't: I'm not proposing recoding anything or rewriting anything or doing any work here beyond changing my use of language as it's convenient for me to do so.
Actually I'm not sure. Anyway, anecdotally, I got into a disagreement with somebody yesterday over what a rational agent would do to find out what somebody had for breakfast. I said that in most cases they would just ask, but the person with whom I was speaking said that they would cut the person open to see what they ate. When I said that this would lead to the agent getting arrested, the person fell back on the idea that when asked the rational agent would give no answer about what the person had for breakfast, since the didn't look inside and see. I rejected this because that would make me, as someone who would just ask, better at updating towards the truth (of what the people had for breakfast) than the rational agent.
This rambling summary of our disagreement could have been avoided if I had just been using the word "optimal" or some other term.
P.S. I think many of the points about the word "optimal" being sub-optimal are good ones, but I think it might be worth looking for a better term than "rational". On the other hand, while "optimal" may not be the optimal word to choose, it could still be the rational one.
Perhaps the optimal way to find out is cutting them open, too. At least if you optimise for certainty of the answer and ignore the side-effects as arrests, ethics and disgust. People can have silly preconceptions of rationality, people can have silly preconceptions of optimality as well (or perhaps propensity to argue about silly things in general).