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

41
1. Aquinas’s General Approach to Cognition
Sometimes it happens that we do not know or are not certain whether something exists,
when for example we have an idea of something but its existence is not obvious to our
senses. In this case, we first ask if what we know confusedly (at least only by name) 31
exists at all (an sit). 32 For example: “does the Minotaur exist?” or “does God exist?” At
first, a nominal definition suffices, i.e. what a given word signifies (ratio nominis or
quid nominis). 33 Thus a question like “does biltrix exist?” does not make sense if we
have no idea whether the word “biltrix” has any signification (to my knowledge, it has
not, at least in English). To state a philosophical or scientific problem we should first
know a language and the significations of words. Yet if anything is to be discovered,
this nominal definition should only be a starting point toward the knowledge of real
things, and to pass from what is known superficially to a deeper and better knowledge.
To know the significations of words is a kind of pre-scientific knowledge. Knowledge
of things as they really are is the main purpose of cognitive project for Aristotle and
Aquinas. It is important to note here that the answer to this first question (as to every
philosophical question) concerns our intellectual judgment and not sensation, 34 although
according to Aristotle and Aquinas no intellectual judgment is possible without some
reference to the sensory existential data.
Knowing that something exists (because it is obvious or because we answered
the first question), we can pursue our questioning to know better what this something is
deficeret, et ideo circa hoc nichil quereremus, nec si est nec propter quid est, set simul utrumque nobis
fieret manifestum” (ibid., p. 177, lin. 296-307]).
31 “Ante quam sciatur de aliquo an sit, non potest proprie sciri de eo quid est (non entium enim non sunt
diffinitiones), unde questio ‘an est’ precedit questionem ‘quid est’; set non potest ostendi de aliquo an
sit, nisi prius intelligatur quid significatur per nomen” (In Poster., I, 2 [Leon. 1*/2, p. 11, lin. 63-69]).
Cf. STh, I, 2, 2; 1, 7 ad 1; In Boet. De Trin., 6, 4 ad 2.
32 “An res sit, tripliciter cognoscit. Uno modo quia cadit sub sensu. Alio modo ex causis et effectibus
rerum cadentibus sub sensu, sicut ignem ex fumo perpendimus. Tertio modo cognoscit aliquid in
seipso esse ex inclinatione quam habet ad aliquos actus: quam quidem inclinationem cognoscit ex hoc
quod super actus suos reflectitur, dum cognoscit se operari” (Super III Sent., 23, 1, 2 sol.).
33 “De eo enim quod est nobis penitus ignotum, non possumus scire si est aut non. Inuenitur autem aliqua
alia ratio rei preter diffinitionem, que quidem uel est ratio expositiua significationis nominis, uel est
ratio ipsius rei nominatae, altera tamen a diffinitione, quia non significat ‘quid est’ sicut diffinitio, set
forte aliquod accidens” (In Poster., I, 8 [Leon. 1*/2, p. 203, lin. 97-104]).
34 “Sciencia non consistit in cognitione quae est per sensum. Et hoc probat sic. Manifestum est enim
quod sensus cognoscit aliquid tale, et non hoc: non enim obiectum per se sensus est substancia et quod
quid est, set aliqua sensibilis qualitas, puta calidum frigidum album nigrum, et alia huiusmodi;
huiusmodi autem qualitates afficiunt singulares quasdam substancias in determinato loco et tempore
existentes; unde necesse est quod id quod sentitur, sit hoc aliquid, scilicet singularis substancia, et sit
alicubi et nunc, idest in determinato loco et tempore. Ex quo patet quod id quod est uniuersale, non
potest cadere sub sensu: non enim quod est uniuersale determinatur ad hic et nunc, quia iam non esset
uniuersale. Illud enim uniuersale dicimus quod est semper et ubique” (In Poster., I 42 [Leon. 1*/2,
p. 158-159, lin. 83-99). Cf. ibid., lin. 121-215.