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

INTRODUCTION
It is commonly known that the question: Is it possible to infer an “ought” from
an “is”? which means: Is it possible to make the transition from descriptive phrases to
prescriptive ones or from fact to value? is nowhere to be found in St. Thomas’s
writings. Neither do we find the question: Is it possible to base ethics upon a non-value
science or upon some definition of goodness? It seems to some that Aquinas, as a pre-
Enlightenment author, did not see these philosophical traps, which were “discovered”
more than five centuries after his death, and thus he unwittingly committed a massive
initial error which led to the elaboration of a complex, blundering moral theory. For
indeed, if we were simply to ask whether Aquinas inferred moral rules from factual
statements or moved from fact to value, many scholars would reply affirmatively,
despite much recent interpretative acrobatics undertaken to deny this. For a fair number
of people this is unfortunately a sufficient reason to cast such an author aside in order to
prevent the loss of precious time in the study of theories which do not respect the basic
rules of contemporary philosophy and theology. For them, to acknowledge this
movement from fact to value is like acknowledging a pupil’s mistake. It completely
disqualifies the author in question. He is banished from the contemporary world of
serious thinking because the thesis “no ‘ought’ from ‘is’” is one of the dogmas of
modern thinking and the “naturalistic fallacy” remains a serious objection in the
evaluations of meta-ethical theories.
This disqualification and banishment may, however, be precipitate. One can
rightly ask, for example, what it means for Aquinas to “infer.” In particular, one can ask