|Aquinas Day by Day: Logic of Concepts: Properties Used in Place of Essential Difference|
Aquinas’ Topic: Logic of Concepts: Properties Used in Place of Essential Difference
Scripture: Psalm 31
“Be a rock of refuge for me, a mighty stronghold to save me, for you are my rock, my stronghold.”
Aquinas’ text: De ente et essentia, c. 5, De veritate 10.1 ad 6m
In speaking about essence and existence in angels and material substances, Br. Thomas here notes that the substantial differences of both kinds of things are hidden from human knowers. So we use material things, at least, we use their properties as an empirical base from which we try to discern their natures.
From De ente et essentia:
Since in these substances [“created intelligences,” angels and human souls], quiddity is not the same as existence [esse] they are placed in a category, and for this reason genus and species and difference are found in them. But their proper differences are hidden from us. For in sensible things the essential differences of sensible things are also hidden from us, so they are signified by accidental differences, which arise from essential differences, as a cause is signified by its effect. For example, “biped” is given as the difference of a human [as Aristotle invariably does]. But the proper accidents of immaterial substances are unknown to us, so we cannot signify their differences either through themselves or through accidental differences.
From De veritate:
Since, according to the Philosopher, the substantial differences of things are unknown to us, in place of them those devising definitions sometimes use accidental differences because accidents designate or make known an essence, as proper effects make known a cause. Therefore, “sensible,” when given as the constitutive difference of “animal,” is not taken from sense as it denominates a power but as it denominates the essence of the soul from which that power flows. The same is true of “rational” or of “what has mind.”
Ad sextum dicendum, quod secundum philosophum in VIII Metaph., quia substantiales rerum differentiae sunt nobis ignotae, loco earum interdum definientes accidentalibus utuntur, secundum quod ipsa accidentia designant vel notificant essentiam, ut proprii effectus notificant causam: unde sensibile, secundum quod est differentia constitutiva animalis, non sumitur a sensu prout nominat potentiam, sed prout nominat ipsam animae essentiam, a qua talis potentia fluit. Et similiter est de rationali, vel de eo quod est habens mentem.
Et quia in istis substantiis quiditas non est idem quod esse, ideo sunt ordinabiles in praedicamento, et propter hoc invenitur in eis genus et species et differentia, quamvis earum differentiae propriae nobis occultae sint. In rebus enim sensibilibus etiam ipsae differentiae essentiales ignotae sunt, unde significantur per differentias accidentales, quae ex essentialibus oriuntur, sicut causa significatur per suum effectum, sicut bipes ponitur differentia hominis. Accidentia autem propria substantiarum immaterialium nobis ignota sunt; unde differentiae earum nec per se nec per accidentales differentias a nobis significari possunt.
[Introductions and translations © R.E. Houser]