Peter Singer, in NYRB. asks whether "some moral judgments [are] true and others false," and notes that this hinges on a more fundamental philosophical question: "Are there objective reasons for action?"
"By 'objective reasons for action,' philosophers mean reasons that hold for everyone, regardless of their preferences, attitudes, or desires"
"The view that there are no objective reasons for action was forcefully presented in 1739 by David Hume, who wrote in his Treatise of Human Nature that 'reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.'"
"By 'passions' he meant all kind of desires, including what he called 'calm passions,' such as benevolence, love of life, and kindness to children.' Thse are not the products of reason, he believed, but rather 'instincts originally implanted in our natures.'"
Thomas Nagel mounts a challenge to this in 1970, in his The Possibility of Altruism
he notes that we can be influenced by our own future desires, and extrapolates from this that we could "take an impersonal perspective from which the desires of others also provide us with reason for action"