Not surprisingly, most people here asserted that moral propositions are not under the scope of science. Perhaps it is one of the arguments to support the philosophical independence .
Generally, I agree with what most of the people here said, but I need to expound it further. Empirical inquiry does not solely refer to natural sciences if we are talking about moral philosophy. When we say Empirical or scientific inquiry, we simply refer to a meta-ethical justification stating that physical feelings can correspond to a certain moral value. Thus, hedonism and utilitarianism are forms of empirical justifications, because it equates goodness with pleasures. In a first glimpse, we cannot see any absurdity in that. After all if we are all satisfied, everything is good.
But ethical non-naturalism challenges this ethical justification. Ethical non-naturalism argues that combining pleasures and satisfactions cannot constitute to anything aside from being pleasurable. As such, the term "good" is not a physical property, rather it is an irreducible component of a particular action. Thus, an action should satisfy a certain objective standard to deductively justify the intrinsic goodness of an action. This means that the term good is not empirical and is not synonymous to pleasures, because we will still ask what made pleasures good or right?I am not saying that hedonism is wrong. I am just saying sciences can use hedonism to make morality entirely empirical. But it failed because goodness is not an empirical property.
There are also other attempts to make morality scientific, one of which is through psychology. It argues that external influences shape our moral convictions. According to these people, mind sciences give a better view about morality. However, these sciences only discuss the "motivation to act", and not cannot justify an action. Suppose that a person killed a rabbit, mind scientists would assert that a person did that because there are some uncontrollable impulses that forced that person. But this does not account for any moral value. Is it immoral or moral? Therefore, mind sciences only compliments moral philosophy after it has justified the value of an action. it is sound to say that John became immoral, because his peers are likewise, because we have defined immorality. But it is absurd to say that John is influenced by his peers to kill, thus killing is immoral.