{ 1 } - emotivism to clarify ways to criticize moral feelings.
{ 2 } - the divine command theory to clarify the golden rule (which is part of all the great world religions).
{ 3 } - the ideal observer theory to clarify various qualities of ideal moral thinking (like consistency and impartiality).
{ 4 } - intuitionism to clarify ways to criticize intuitions.
{ 5 } - utilitarianism to clarify principles (like impartiality and the golden rule) that are useful in promoting the good of society.
{ 6 } - all of the above.

Formal ethics can provide tools of ethical thinking that are useful to a wide range of different approaches.