My purpose in this essay is to explain and discuss the importance of the “moral twin earth” argument. This theory focuses on the argument first proposed by Hare, which states that in order to have a genuine moral disagreement there needs to be a common understanding of the concept in question. This theory holds importance because it openly refutes Cornell realism, which denies that moral terms, like ‘right’, are synonymous to any non-moral terms that may be part of the properties that ‘right’ picks out; the properties that are attached to moral terms, like ‘right’ are responsible for their usage. Thus, the goal is to show how the “moral twin earth” argument undermines the idea that moral terms refer to some natural properties of actions, which in turn regulate our moral practices.
The “moral twin earth” thought experiment says that we are to imagine that all Earth human species uses of the word ‘good’ (‘good-E’) entail the natural property, which makes things ‘good’ according to a normative consequentialist theory, let’s say the theory of maximizing happiness. The Earth human species would adopt any moral theory that allowed maximizing happiness as good-making.
Next, imagine that in a separate galaxy there exists a land, Moral Twin Earth. Moral twin Earth is so close to being identical to Earth; the species of twin Earth speak a language that is linguistically and semantically identical to the one Earth species speak, English. Additionally and most importantly, moral terms like ‘good’, ‘bad’, ‘right’ and ‘wrong’ have the same functional properties that they do on Earth. (Horgan & Timmons 1992) The twins use these moral terms to figure out certain actions. For instance, they try to do things to which they apply ‘good’; and they feel happiness and approval when others perform such actions. (Horgan & Timmons 1992) However, despite these similarities there is one intrinsic difference between the two worlds. Twin Earth uses of ‘good’ (‘good-T’) entail the distinctive property that is good-making in terms of a non-consequentialist theory, say not treating others a mere means. If the twin earth species were to adopt any moral theory, they would adopt one, which allowed not treating others as a mere means.
Now, let’s consider and apply the following action. A doctor is seeing a patient for a regular check-up. The doctor looks at the patient’s files and notices that he carries a rare blood type. The doctor decides to extract the equivalent 1-pint of blood to donate it to another patient that is in grave need for the transfusion. When the patient asks why so much blood, the doctor responds by saying that it is for tests. The Earth human, when asked to contemplate the blood transfusion is inclined to say that the ‘act of...