[4.9.4] St Thomas Aquinas on the Classification of Sciences

St Thomas Aquinas ( “Doctor Angelicus”, 1225 – 1274 AD), in his book On The Divisions and Methods of the Sciences: Questions V and VI of his Commentary on the De Trinitate of Boethius writes about the division of sciences (see also [1.3.10])

  • Sciences can be speculative or practical, depending on their relation to truth. Speculative sciences contemplate, while practical sciences apply truth.
  • We can analyze the object of study of the speculative sciences based on their dependence on the existence and understanding of matter and motion.
  • Based on this analysis, the complete list of speculative sciences is physics, mathematics, and metaphysics.
  • Ethics, economics and politics are practical sciences.

The following OntoUML diagram presents Aquinas’s division of sciences:

Aquinas on the division of sciences
ClassDescriptionRelations
Science“There are [..] two distinct classes of science: speculative science and practical science. Speculative sciences are those that contemplate truth whereas practical sciences are those that apply truth for some practical purpose. The sciences are then further distinguished through differentiating their various subject-matters.”studies SubjectMatter
Understanding“Working within the Aristotelian tradition, Thomas holds that something is understood when it is separated from matter and is necessary to thing in some respect. For instance, when we understand the nature of a tree, what we understand is not primarily the matter that goes to constitute the tree in question, but what it is to be a tree, or the structuring principle of the matter that so organizes it and specifies it as a tree rather than a plant. Furthermore, assuming our understanding is correct, when we understand a thing to be a tree, we do not understand it to be a dog, or a horse, or a cat. Thus, in our understanding of a tree, we understand that which is necessary for the tree to be a tree, and not of anything that is not a tree. Hence, our understanding of a thing is separated from its matter and is necessary to it in some respect. Now, what is in motion is not necessary, since what is in motion can change. Thus, the degree to which we have understood something is conditional upon the degree to which it is separated from matter and motion. It follows then that speculative objects, the subject-matter of the speculative-sciences, insofar as they are what are understood, will be separated from matter and motion to some degree. Any distinctions that obtain amongst speculative objects will in turn signify distinctions amongst the sciences that consider those objects; and we can find distinctions amongst speculative objects based upon their disposition towards matter and motion.”relates between Science and SubjectMatter
PracticalSciencepractical sciences are those that apply truth for some practical purpose.”subkind of Science; applies Truth
Ethics; Economics PoliticsEthics, economics and politics are practical sciences.subkind of PracticalScience
SpeculativeScienceSpeculative sciences are those that contemplate truth […]
There are three divisions that can apply to speculative objects, thereby permitting us to differentiate the sciences [to physics, mathematics and metaphysics…]
Thomas takes this division of the speculative sciences as exhaustive. For Thomas, there could be no fourth speculative science; the reason for this is that the subject-matter of such a science would have to be those things that depend on matter and motion for their being understood but not for their being, for all other combinations have been exhausted. Now, if a thing depends on matter and motion for its being understood but not for its being, then matter and motion would be put into its definition, which defines a thing as it exists. But if a thing’s existence is so defined as to include matter and motion, then it follows that it depends on matter and motion for its being; for it cannot be understood to be without matter and motion. Hence, all things that include matter and motion in their definitions are dependent on matter and motion for their being, but not all things that depend on matter and motion for their being depend on matter and motion for their being understood. There could be no fourth speculative science since there is no fourth class of speculative objects depending on matter and motion for their being understood but not for their being. Thomas thus sees this threefold division of the speculative sciences as an exhaustive one.”
subkind of Science; contemplates Truth
Physics“(i) physical science considers those things that depend on matter and motion both for their being and for their being understood”subkind of SpeculativeScience; studies ObjectOfStudy OfPhysics
Mathematics “(ii) mathematics considers those things that depend on matter and motion for their being but not for their being understood”subkind of SpeculativeScience; studies ObjectOfStudy OfMathematics
Metaphysics“(iii) metaphysics or theology deals with those things that depend on matter and motion neither for their being nor for their being understood.”subkind of SpeculativeScience; studies ObjectOfStudy OfMetaphysics
SubjectMatter“In order to ascertain the subject-matter of any particular science, Thomas distinguishes between the different intellectual operations that we use when engaged in some particular scientific endeavor. Broadly speaking, these fall into two categories: the speculative and the practical. Concerning some sciences, the intellect is merely speculative  by contemplating the truth of some particular subject-matter; while concerning other sciences, the intellect is practical, by  ascertaining the truth and seeking to apply. There are thus correspondingly two distinct classes of science: speculative science and practical science. Speculative sciences are those that contemplate truth whereas practical sciences are those that apply truth for some practical purpose. The sciences are then further distinguished through differentiating their various subject-matters.”
ObjectOfStudy OfPhysics“(i) there is a class of speculative objects [object of study of physics] that are dependent on matter and motion both for their being and for their being understood, for instance, human beings cannot be without matter, and they cannot be understood without their constituent matter (flesh and bones)”subkind of SubjectMatter
ObjectOfStudy OfMathematics“(ii) there is a class of speculative objects [object of study of mathemathics] that depend on matter and motion for their being, but not for their being understood, for instance, we can understand lines, numbers, and points without thereby understanding the matter in which they are found, yet such things cannot be without matter”subkind of SubjectMatter
ObjectOfStudy OfMetaphysics” (iii) there is a class of speculative objects [object of study of metaphysics] that depend on matter and motion neither for their being nor for their being understood.
[…] As it is a purely rational science, not dependent on or presupposing the truths of revelation, metaphysics will be a study of the neutrally immaterial aspects of things, that is, a study of those modes of being that apply to all beings, whether they are material or immaterial. 
Thomas does not adopt the Aristotelian phrase (being qua being) as the subject-matter of metaphysics, he offers his own term. According to Thomas, ens commune (common being) is the proper subject-matter of metaphysics. Through an investigation of ens commune, an investigation into the aspects of being common to all beings, the metaphysician may indeed come to a knowledge of the causes of being and might thereby be led to the affirmation of divine being, but this is only at the end of the metaphysical inquiry, not at the beginning.”
subkind of SubjectMatter

Sources

  • All citations from:  Kerr, Gaven : “Aquinas: Metaphysics”Internet Encyclopedia of Philosophy
  • McInerny, Ralph and John O’Callaghan, “Saint Thomas Aquinas”The Stanford Encyclopedia of Philosophy (Summer 2018 Edition), Edward N. Zalta (ed.)
  • The Cambridge Companion to Aquinas, CAMBRIDGE UNIVERSITY PRESS, Edited by  Norman Kretzmann and Eleonore Stump, 2010

First published: 01/10/2020

[3.3.6] Ibn Sina on Scientific Method and Demonstration

In the UML Activity Diagram below, I propose a reconstruction of the scientific “business” process based on Ibn Sina’s (Avicenna, 980-1037 AD) ideas about scientific inquiry elaborated in his works Kitāb al-Burhân, Najâh.
Here are some highlights of his ideas:

  • Sense perception with the involvement of the 5 external and internal senses (see [3.3.3]) is the starting point of the scientific process.
  • Abstraction, Induction and Methodic Experience are the activities to acquire First Principles. Syllogisms (see [3.3.5]) and actualization of the Intellect with Forms provided by First Intellect (see [3.3.3], [3.3.4]) both have their roles in these activities.
  • After First Principles are available, new knowledge can be reached with deduction, using syllogisms (see [3.3.5]).
Avicenna on scientific process
ACTIVITY/ActionDescription
Obtain perceptibles of an object with Sense Perception“the universal premises of demonstration and their principles are obtained only through sensory perception…” (McGinnis (2008), cites Avicenna)
ABSTRACTION“by acquiring the phantasmata (خيالات) of the singular terms through the intermediacy of [sensory perception] in order that the intellectual faculty freely acts on them in such a way that it leads to acquiring the universals as singular terms and combining them into a well-formed statement…
[T]he essences perceptible in existence are not in themselves intelligible, but perceptible; however, the intellect makes them so as to be intelligible, because it abstracts their true nature (حقيقتها) from the concomitants of matter…
Thus [the speculative intellect] receives these accidents, but then it extracts them, as if it is peeling away these accidents and setting them to one side, until it arrives at the account in which are common and in which there is no variation and so acquires knowledge of them and conceptualizes them.
The first thing that [the intellect] inquires into is the confused mixture in the phantasm; for it finds accidental and essential features, and among the accidents those which are necessary and those which are not. It then isolates one account after another of the numerous ones mixed together in the phantasm, following them along to the essence. (McGinnis (2008), cites Avicenna)
“this is not Avicenna’s whole story concerning abstraction and acquiring first principles; for as he says later, acquisition of the first principles also involves “a conjunction of the intellect with a light emanated upon the soul and nature from the
agent that is called the ‘Active Intellect’” (McGinnis (2008)).
INDUCTIONAvicenna accepts Aristotle’s view on Induction (see [1.3.8]) however, criticizes it: “Induction has two elements: one involves the sensible content of induction and the other the rational structure of induction, namely, the syllogism associated with induction. If induction is to provide one with the necessary and certain first principles of a science, then the necessity and certainty of the conclusion of an inductive syllogism must be due either to
induction’s sensory element or its rational element or some combination of both. On the one hand, the purported necessity and certainty of induction cannot be known solely through induction’s sensory element; for in good empirical fashion Avicenna
recognizes that necessity and certainty are not direct objects of sensation. On the other hand, if the necessity and certainty are due to induction’s rational component, then the syllogism associated with induction should not be question begging. Yet,
complains Avicenna, in the scientifically interesting cases one of the premises of an induction will be better known than its conclusion, and so the induction is neither informative nor capable of making clear a first principle of a science.” (McGinnis (2008)).
METHODIC EXPERIENCE“Ibn Sînâ’s theory of experimentation is by no means modern, it does move one closer to a modern scientific approach; for it emphasizes both the need to set out carefully the conditions under which experimentation or examination have taken place, as well as the tentativeness of scientific discoveries in the face of new observations…
experimentation involves in part seeking falsifying cases…the exceptions [falsifying cases] would be extremely rare, perhaps observed only once or twice. These rare exceptions might indicate that there is not a causal relation, but they might also indicate that the causal circumstances were more complex than initially supposed…
Experimentation, with its accompanying syllogism, then, occasions certainty…
although experimentation cannot provide “absolute” principles, the natural scientist can use experimentation to discover “conditional,” universal principles, which can function as first principles in a science.” (McGinnis (2003)).
Check certainty condition (true/ real, necessary) “Avicenna’s ‘certainty condition’ (يقين),… includes both being true or real (الحقّ) and necessary (الضروري)” (McGinnis (2008)).
First Priciple AcquiredIf certainty condition is fulfilled.
DEDUCTION“A demonstration according to Avicenna is ‘a syllogism constituting certainty’. In other words, it is a deduction beginning with premises that are certain or necessary that concludes that not only such and such is the case, but that such and such cannot not be the case. Thus, demonstrative knowledge involves possessing a syllogism that makes clear the necessity
or inevitableness obtaining between the subject and predicate terms of its conclusion. In addition, Avicenna divides demonstrative knowledge itself into two categories depending upon the type of demonstration employed. Thus there is the demonstration propter quid, or demonstration giving ‘the reason why’ ( برهان لِمَ ) and the demonstration quia, or demonstration giving ‘the fact that’ (برهان لأن ).” (McGinnis (2008)).

Sources

  • McGinnis,  Jon, “Avicenna’s Naturalized Epistemology and Scientific Method”, chapter from: The Unity of Science in the Arabic Tradition: Science, Logic, Epistemology and their Interactions, springer, 2008
  • McGinnis, Jon, “Scientific Methodologies in Medieval Islam”, Journal of the History of Philosophy. 41. 307-327. 10.1353/hph.2003.0033., 2003

First published: 05/09/2019