According to this view some ethical terms are verbally indefinable. Even if right can be defined in terms of say as productive of the most good, at least good in its turn cannot be defined.
As Sidgwick said, what definition can we give of ought right and other to terms to expressing the same fundamental motion? To this I should answer that the motion which these terms have in common is too elementary to admit of any definition. The motion can not be resolved into any more simple motion.
Non-naturalism does not say that ethical terms cannot be defined by means of other ethical terms. For example desirable can be translated into ought to be approved. But this is only to define one ethical term by using another.
What non naturalism says is that one ethical term cannot be defined exclusively by means of non-ethical ones. Such words as good, right and ought are so fundamental in ethics that there are no other words by means of which to define them.
Moore says, good is verbally indefinable, just as other words in our language. Such as yellow and pleasure are verbally indefinable, ‘To identify good with any ‘natural objects’. Moore calls this as naturalistic fallacy.
It is true that pleasure cannot be defined verbally. But it can be defined obstensively ‘that is how it enters our language and its meaning is understood, by many people. But good like ‘red’, ‘pleasure’ does not stand for an experience.
One may have an experience that we call felling well. But that is not what good means in ethics. Ethical sentences have a meaning that is not reducible to nonethical ones, just as sentences in mathematics. Using terms like number, plus and equals are not reducible to any non-mathematical sentences.
Some one may ask, what are ethical sentences about? They are not about the speakers feeling of approval of something, not about the feeling or attitude, not about God’s attitude towards X, nor about consequences of X, nor about any other property of X. They are about what is good, what is valuable what is right, what one ought to do. But one may ask how is one to know whether ethical propositions are true? The non-naturalist says there is no empirical observation and no mathematical or logical calculation that will enable us to discover their truth.