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

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Introduction
they simply commit the straw man fallacy. Today, these accusations are often an
obstacle to reading or taking authors such as Aquinas seriously.
Given that there are disparate interpretations of Aquinas’s texts, an appropriate
interpretative key will also be sought, in order to protect our reading from at least some
errors. Taking into account the historical context of Aquinas’s writings and their
character, as well as Aquinas’s repeated statements, we will look to the order of
learning to guide our research.
Since it is claimed that the transition from “is” to “ought” is “logically illicit” (or
that the “Is/Ought Thesis” contains a logical sub-thesis), I will present in Chapter 2
some elements of the logic used by Aquinas, as well as examining the place of logic in
the order of learning. This will reveal his specific understanding of logic and its role in
the whole philosophical-scientific enterprise.
In Chapter 3, I will proceed in exploring some fundamental topics of Aquinas’s
logic, especially his semantics and the inherence theory of predication. This will enable
us to see the direction of St. Thomas’s possible answer to the semantic sub-thesis of the
“Is/Ought Thesis” in Moore’s reformulation.
Without drawing hasty conclusions, we will continue in Chapter 4 to manifest
still another part of Aquinas’s logic that is essential to our purposes. This part of his
logic is a general methodology for every science, including moral science and theology.
It consists in an extensive theory of demonstration and exhibits the rules for causal
explanation. We will see how causal explanation, and especially the use of final cause
in demonstrating purposeful facts or events, is made possible thanks to semantic
presuppositions presented in Chapter 3. The question of first indemonstrable principles
will also be briefly discussed.
Building upon what is addressed in the first part, on logic, the second part begins
with Chapter 5 with the investigation of possibilities of constructing an “is.”
Specifically, I seek a science that constructs such a human “is” which might provide
a basis for infering an “ought.” I point at natural science as this science in which we
might, in the most proper and comprehensive way, present what the human being is.
Next, in Chapter 6, I delve into the question of the specificity of method in
natural science conditioned by its object and principles. Principles of natural things are
shown in terms of basic hylomorphism, the notion of nature itself is briefly explained,
as also the principles of natural science are revealed in the analysis of formal, material,
efficient and final causes. Already here the topic of goodness appears and is