This makes quasi-realism a form of non-cognitivism or expressivism. Quasi-realism stands in opposition to other forms of non-cognitivism (such as emotivism and universal prescriptivism), as well as to all forms of cognitivism (including both objectivist theories such as moral realism, and subjectivist theories such as moral relativism).
Simon Blackburn derived this stance from a Humean account of the origin of our moral opinions, adapting Hume's genealogical account in the light of evolutionary game theory. To support his case, Blackburn has issued a challenge, Blackburn's Challenge, to anyone who can explain how two situations can demand different ethical responses without referring to a difference in the situations themselves. Because this challenge is effectively unmeetable, Blackburn argues that there must be a realist component in our notions of ethics.
However, argues Blackburn, ethics cannot be entirely realist either, for this would not allow for phenomena such as the gradual development of ethical positions over time. In his 1998 book, Ruling Passions, Blackburn likens ethics to Neurath's boat, which can be changed plank by plank over time, but cannot be refitted all at once for risk of sinking. Similarly, Blackburn's theory can explain the co-existence of rival ethical theories, for example as a result of differing cultural traditions - his theory allows both to be legitimate, despite their mutual contradictions, without dismissing both views through relativism. Thus, Blackburn's theory of quasi-realism provides a coherent account of ethical pluralism. It also answers John Mackie's concerns, presented in his argument from queerness, about the apparently contradictory nature of ethics.
Despite gaining some of the better qualities of the component theories from which it is derived, quasi-realism also picks up vulnerabilities from these different components, too. Thus, it is criticised in some of the ways that moral realism is criticised, for example by Fictionalism (see below); it is also attacked along with expressivism and other non-cognitive theories (indeed it has been regarded by some as a sub-category of expressivism).
This means that, though the moral fictionalist is in some ways having cake and eating it, the quasi-realist has a seemingly even more difficult position to defend. They may feel secure in disagreeing with Bentham that talk of human rights is "nonsense upon stilts" but they would also argue that such rights could not be said to exist in a realist sense. Quasi-realism captures in some important ways the structure of our ethical experience of the world and why we can assert claims such as "It is wrong to be cruel to children" as if they were facts even though they do not share the properties of facts; namely the inference of independent truth-values.
From this position, Blackburn's "way forward" is to re-assert Hume's 'common point of view', or the ethical discourse common to mankind. Blackburn's thought is that though relativists and realists can agree that certain statements are true within a certain discourse, a quasi-realist investigates why such discourses have the structures that they do.