  The simplest reason to suppose that preferences are basic is that they are readily introspected and acted upon, whereas desires with specific strengths are not. I can tell that I prefer securing my father's health to doing the laundry, and I know which I would choose if it came to a choice. But can I introspect the degree to which I prefer my father's health over clean laundry? Perhaps not. And if I cannot, perhaps this is because I have introspective access to the most basic psychological facts only, and these are facts about simple pairwise preferences. As von Neumann and Morgenstern write, “every measurement—or rather every claim of measurability—must ultimately be based on some immediate sensation, which possibly cannot and certainly need not be analyzed any further. In the case of utility the immediate sensation of preference—of one object or aggregate of objects as against another—provides this basis” (1944, 16).