Metaethics is the branch of ethics devoted to understanding the nature of the components of ethics. It seeks answers for questions like "Are moral judgments objective or subjective, relative or absolute?" and "Do moral facts exist?", termed second-order moral questions. It is a field in rapid development, permitted by the developing field of Neuroscience. Rationality is well suited to analyzing the field of metaethics. Metaethics is also critical to the development of a Friendly Artificial Intelligence.
Luke Muehlhauser has begun a sequence, No-Nonsense Metaethics, and has claimed many of the questions of metaethics can be answered today using modern neuroscience and rationality. He explains how conventional metaethics or "Austere Metaethics" is capable of, after assuming a definition of 'right', choosing the right action given a situation - but useless without assuming some criteria for 'right'. He proposes instead "Empathic Metaethics" which utilizes your underlying cognitive algorithms to understand what you think 'right' means, helps clarify any emotional and cognitive contradictions in it, and then tells you what the right thing to do is, according to your definition of right.