Ideas from 'De Ente et Essentia (Being and Essence)' by Thomas Aquinas [1267], by Theme Structure

[found in 'Selected Philosophical Writings' by Aquinas,Thomas (ed/tr McDermott,Timothy) [OUP 1993,0-19-282946-7]].

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2. Reason / D. Definition / 5. Genus and Differentia
The definitions expressing identity are used to sort things
                        Full Idea: What sorts things into their proper genus and species are the definitions that express what they are.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92)
                        A reaction: This is straight from Aristotle, though Aristotle's view is a little more complex, I think. If the definitions 'express what they are', then definitions seem to specify the essence.
If definitions must be general, and general terms can't individuate, then Socrates can't be defined
                        Full Idea: Socrates has no definition if definitions by their nature must be in purely general terms, and if no purely general terms can succeed in uniquely singling out this signated matter.
                        From: report of Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], 23) by Cover,J/O'Leary-Hawthorne,J - Substance and Individuation in Leibniz 1.1.2
                        A reaction: There seem to be two models. That general terms actually individuate the matter of Socrates, or that they cross-reference to (so to speak) define Socrates 'by elimination', as the only individual that fits. But the latter is a poor definition.
7. Existence / A. Nature of Existence / 3. Being / e. Being and nothing
If affirmative propositions express being, we affirm about what is absent
                        Full Idea: If being is what makes propositions true, then anything we can express in an affirmative proposition, however unreal, is said to be; so lacks and absences are, since we say that absences are opposed to presences, and blindness exists in an eye.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92)
                        A reaction: See Idea 11194 for the alternative Aristotelian approach to being, according to categories. Do absences and lacks have real essences, or causal properties? The absence of the sentry may cause the loss of the city.
8. Modes of Existence / B. Properties / 8. Properties as Modes
Properties have an incomplete essence, with definitions referring to their subject
                        Full Idea: Incidental properties have an incomplete essence, and need to refer in their definitions to their subject, lying outside their own genus.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.93)
                        A reaction: These are 'incidental' properties, but it is a nice question whether properties have essences. Presumably they must have if they are universals, or platonic Forms. The notion of being 'strong' can be defined without specific examples.
8. Modes of Existence / D. Universals / 6. Platonic Forms / d. Forms critiques
If the form of 'human' contains 'many', Socrates isn't human; if it contains 'one', Socrates is Plato
                        Full Idea: If (in the Platonic view) manyness was contained in humanness it could never be one as it is in Socrates, and if oneness was part of its definition then Socrates would be Plato and the nature couldn't be realised more than once.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.100)
                        A reaction: I suppose the reply is that since we are trying to explain one-over-many, then this unusual combination of both manyness and oneness is precisely what distinguishes forms from other ideas.
9. Objects / A. Existence of Objects / 5. Individuation / a. Individuation
The principle of diversity for corporeal substances is their matter
                        Full Idea: In the view of Aquinas, while substantial form is the ultimate ground of identity and difference of angels, it is matter that provides a principle of diversity in the case of corporeal substances.
                        From: report of Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267]) by Cover,J/O'Leary-Hawthorne,J - Substance and Individuation in Leibniz 5.2.3
                        A reaction: This is at least as good a proposal as their apatial location. There is more chance of reidentifying matter than of precisely reidentifying a spatial location. Two indistinguishable spheres remain the classic problem case (of Max Black, Idea 10195)
9. Objects / D. Essence of Objects / 1. Essences of Objects
It is by having essence that things exist
                        Full Idea: It is by having essence that things exist.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.94)
                        A reaction: Compare Idea 11199, which gives a fuller picture. This idea seems to suggest essence as the cause of existence, which sounds wrong. Perhaps essence is a necessary condition of existence, but it is necessary that nothing indeterminate can exist?
9. Objects / D. Essence of Objects / 2. Types of Essence
Specific individual essence is defined by material, and generic essence is defined by form
                        Full Idea: Specific essence differs from generic essence by being demarcated: individuals are demarcated within species by dimensionally defined material, but species within genus by a defining differentiation taken from the form.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.95)
                        A reaction: It clearly won't be enough to define an individual just to define its material and its shape. The material might also be essential to the genus, as when defining fire. Probably not very helpful.
9. Objects / D. Essence of Objects / 4. Essence as Definition
The definition of a physical object must include the material as well as the form
                        Full Idea: Form alone cannot be a composite substance's essence. For a thing's essence is expressed by its definition, and unless the definition of a physical substance included both form and material, the definition wouldn't differ from mathematical objects.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.93)
                        A reaction: This is the sort of thoroughly sensible remark that you only get from the greatest philosophers. Minor philosophers fall in love with things like forms, and then try to use them to explain everything.
9. Objects / D. Essence of Objects / 5. Essence as Kind
Essence is something in common between the natures which sort things into categories
                        Full Idea: Since being as belonging to a category expresses the 'isness' of things, and belongs to all ten Aristotelian categories, essence must be something all the natures that sort different beings into genera and species have in common.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92)
                        A reaction: I like this because it is the essence which does the sorting, not the sorting which defines the essence (which seems to me to be a deep and widespread confusion).
9. Objects / D. Essence of Objects / 6. Essence as Unifier
A simple substance is its own essence
                        Full Idea: A simple substance is its own essence.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.103)
                        A reaction: Aquinas takes complex substances to have their essences in various ways, but this thought is the basis of all essence. Presumably the Greek word 'ousia' names the key ingredient.
14. Science / D. Explanation / 2. Types of Explanation / k. Explanations by essence
Definition of essence makes things understandable
                        Full Idea: It is definition of essence that makes things understandable.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92)
                        A reaction: The aim of philosophy is understanding, which is achieved by successful explanation. I totally agree with this Aristotelian view, so neatly summarised by Aquinas.
19. Language / C. Assigning Meanings / 3. Predicates
The mind constructs complete attributions, based on the unified elements of the real world
                        Full Idea: Attribution is something mind brings to completion by constructing propositional connections and disconnections, basing itself on real-world unity possessed by the things being attributed to one another.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.102)
                        A reaction: This compromise story seems to me to be exactly right. I take it that we respond to the real joints of nature, but using thought and language which is riddled with convention.
26. Natural Theory / C. Causation / 5. Direction of causation
A cause can exist without its effect, but the effect cannot exist without its cause
                        Full Idea: When things are so related that one causes the other to exist, the cause can exist without what it causes but not vice versa.
                        From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.103)
                        A reaction: This is open to question, if causes are supposed to be sufficient for effects. Presumably Aquinas would support the view that if the cause had not been, the effect would not have happened. But the current idea indicates the priority relation.