Reasons and Rationality

What is it to be to rational? Some say to be rational is to respond to reasons. Likewise, some may think that if one does something they have no reason to do, then they are irrational. But there are many cases in which someone does something they have no reason to, in which it seems they are completely rational (e.g. I believe there is a glass of gin in front of me and I want some gin, so I drink; but unbeknownst to me the glass is full of petrol. I have no reason to drink the petrol but it seems that my doing so was completely rational). I think a lot of these problems tend to trade on the ambiguity of the English word 'reason'. This is often acknowledged by philosophers in the literature but it is also often underappreciated or ignored. To combat this we should all internalize this bit from a recent paper by John Broome. I doubt that anyone would disagree with this.

"“Many philosophers unhesitatingly assume there is some conceptual connection between rationality and reasons. More specifically, they assume that acting contrary to reasons is irrational. Why make this assumption? There are certainly connections between the words 'rational'’ and '‘reason'. For one thing, they have the same Latin root. But, although etymology can be suggestive, it gives no real ground for thinking there is a connection between the concepts. More confusingly, the word '‘reason'’ has various senses, and in one of them it refers to the faculty of reason. 'Reason'’ used this way is a mass noun - a noun that has no plural. Our faculty of rationality is plainly part of, or perhaps all of, our faculty of reason. So there is certainly a conceptual connection between rationality and reason in this sense. But the word '‘reason'...does not have that sense. It is a count noun - a noun that has a plural. Its plural is 'reasons'’. Just because rationality is conceptually connected with the faculty of reason, it does not follow that it is conceptually connected with reasons." - John Broome, "Is Rationality Normative"