 Philosophers such as Hume and Priestly were eager to apply Newton’s methods to the moral domain. Reid, however, viewed attempts to use Newtonian methods to understand the moral domain as mistaken—not, once again, because he viewed Newtonian science as suspect, but because he held that Newton’s methods themselves require this. That said, we have seen that there is a sense in which Reid believes that human action is law-governed. We can regulate our behavior by reference to the rational principles of action. Earlier we saw that these principles are of two kinds: They concern our good on the whole and duty. Reid holds that these principles stand in a certain kind of relation to one another. We can better identify this relation by having the notion of motivational primacy before us.