Did St. Thomas Aquinas Justify the Transition from 'Is' to 'Ought'

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0. A Short History of the Problem
Moore believed that the “Open Question Argument” undermines ethical
naturalism as well as ethical supernaturalism. We encounter this belief in his insistence
that moral facts and properties are sui generis, that is, are neither reducible to nor
derivable from non-moral (scientific or metaphysical) judgments. This is why, he
claims, ethics should be autonomous. Moore denies that ethical issues could be a matter
of empirical enquiry. He also denies that fundamental ethical truths are truths of reason.
His solution consists in discerning a human capacity to grasp fundamental ethical truths
intuitively. We cannot assign any reason that would justify these truths because they are
fundamental and we grasp them intuitively; thus our knowledge of moral truths is not
arrived at by inference from non-moral truths but is founded on the recognition of
certain moral propositions as self-evident. 42 Nonetheless, he holds that normative
judgments are objectively true or false and that fundamental moral judgments ascribe
the property of goodness to states of affairs (placing him in the camp of moral realists).
Moore bases his argument primarily on the semantic assumption that moral and
nonmoral terms are not interdefinable. In this way “naturalistic fallacy” becomes
a reformulation of the “Is/Ought Thesis.” 43 We spoke above about a hidden distinction
in Hume’s formulation of the thesis into the “internalist assumption” and the inferential
gap. Moore seems to offer an equivalent of the second part of the original formulation
(the inferential gap). In David Brink’s analysis, this version of the “Is/Ought Thesis”
might be presented as follows:
Because nonmoral statements consist of (i) synthetic statements expressed by
sentences using no term in its moral sense, and (ii) analytic statements, the is/ought
thesis claims that no moral statement can be deduced from a consistent set of
premises made up entirely of statements of types (i) and (ii). This formulation alows
us to distinguish two subtheses in the is/ought thesis. The logical thesis claims that no
moral statement can be deduced from statements exclusively of type (i). The semantic
thesis claims that there are no type (ii) statements which by themselves, or in
conjunction with type (i) statements, would entail a moral statement. In particular, the
semantic thesis claims that there are no statements asserting relations of implication
between the possession of moral properties and the possession of nonmoral properties
– moral bridge premises – that are analytic. (If we were to deny the existence of
analytic statements, we could construe the is/ought thesis as the claim that no moral
statement can be deduced from a consistent set of premises consisting entirely of
42 Naturalism is characterized by the claim that moral facts are nothing more than familiar facts about the
natural, including social, world. Whereas the proper claim of supernaturalism is that moral facts and
properties are supernatural facts and properties. Some of his philosophical posterity accepted rejection
of ethical naturalism and supernaturalism but did not enter into nonnaturalism. Instead, they claim that
there are no moral facts or properties and have therefore adopted some form of noncognitivism. Cf.
David O. Brink, Moral Realism and the Foundations of Ethics (Cambridge University Press, 1989), p.
156.
43 Cf. ibid., p. 146-147.