Whilst the discussion of Sidgwick made clear a number of features of intuitionism that are important, Sidgwick himself had only a partial acceptance of intuitionist tenets. At the beginning of the 20th century, by contrast, G.E. Moore wrote a work that had a broad effect on the understanding of intuitionism as well as providing a set of methodological guidelines that proved influential within the general practice of ethics. This is Principia Ethica. Moore's book has a number of odd characteristics but key amongst its claims are the following:
1. The notion of "good" is simple and unanalysable meaning by this that it is an ultimate term that cannot be reduced to anything further.
2. The notion of "good" is something quite different from what could be meant by anyone after an enquiry into "the good" as what would fit this notion would be a complex that could be understood in this way due to combination of different types of things together in their notion.
3. The question concerning what kinds of things ought to exist for their own sake or as good in themselves are incapable of proof and this claim that they are incapable of proof is what is meant by claiming that our relationship to such things is one of "intuition".
4. Our sense of what kinds of things ought to be done is something different from any of the above though again it is a question that involves complexes and is best understood in an overall sense, with regard to things not too far distant, to be generally probable, and to involve pluralist conceptions (i.e., a number of things not reducible to each other).
The peculiarities of the combination of these positions in the work should be fairly clear but the emphasis on pluralism in connection with an epistemic thesis that denies that the ultimate question about ethics is one that can be captured by reference to ends separable from the sense of what is "good" (albeit combined with a rule-consequentialism concerning conduct) do indicate a mixed response to ethics that helps to bring out the basis for the muddle that later becomes the antithesis between "deontology" and "teleology".