Usor:Wmdiem/Philosophiae Thomisticae introductio ingredientibus

This is to be a brief introduction to Thomistic philosoical thought for those unfamiliar with scholastic philosophy. It is intended as a compliment to the Glossarium Thomisticum, that is as a more systematic exposition of the ideas underlying the words defined therein.

Natural Philosophy

Aquians's natural philosophy is largely an attempt to explain change in the physical world. Aquians starts his first work on natural philosophy (the De principiis naturae, an opisculum written to a fellow student), by noticing that there are things which are said to be, and things which are said to be able to be, but are not. The former corresponds to the actual, and the latter corresponds to the potential. Natural things are a composite of matter and form; They have potency by virtue of their matter but are made actual through their forms. Forms, thus, just are whatever makes a thing actually be a certain way. Aquians follows the Aristotelian tradition in positing four causes: material, formal, agent (active), and final (end). Every non-accidental natural change has these four causes. The matter is the initial potency for the end state. The form is what must be added to the matter to bring about the end state. The agent is that thing which brings about the change. The end is that which is to be brough about and for the sake of which the agent acts. Aquinas sees two essentially different types of change to be explained: Substantial and accidental. A substatial change is a change in which one substance is destroyed (corrupted) and a new substance is made (generated), where Aquinas means by substance a thing existing in its own right. An accidental change is likewise when an accident is generated, an accident being something that exists, not on its own, but in another, e.g., whiteness which exists not alone but only in some thing that is white. In a substantial change matter is used in a strong sense, that potency which underlies all material being. In an accidental change Aquinas will say that matter is used only loosely to refer to the substance that the accident come to be in, stictly called a subject. Curucial to Aquians's natural philosophy is the conviction that natural things, physical substances, have natures (that is a principle of acting), and that natures, as Aristotle held, act for ends. This he says is evident because natural things act always or often in the same way, so as to bring about particular ends (e.g., the plant turning toward sun to optimize exposure, animals protecting their young, etc.). Aquinas will even say natural things intend (intendere, tend toward) ends, though he realises that this does not mean they know or reason about these ends, only that they consistently tend to certain ends.

Logic

The purpose of logic according to Aquinas is to aid scientific reasoning. Because science aims at universal truth, logic does not treat individuals or particulars directly. A step in an apodictic scientific argument is a syllogism, which has two premises and a conclusion, each composed of two terms joined by a copula. The terms are the subject (or minor term), predicate (or major term), and middle. The subject is the term that is the subject in the conclusion; The predicate is the predicate of the conclusion; The middle does not appear in the conclusion. The two premises (called the Major and the Minor) both contain the middle term, but the Major contains the predicate and the Minor contains the subject. Thus in all x's are y's, all y's are z's, therefore all x's are z's, the subject is x and the predicate is z, while the middle is y. Further the Minor is all x's are y's (contains the subject and middle), the Major is all y's are z's (contains the predicate and the middle).

Further because scientific knowledge is to be certian, the ideal logical argument is a demonstation (demonstratio) which is a syllogism in which the middle term is a definition (e.g., 'all x's are y's and all y's are z's.' where y is the definition of x).

This highlights an important aspect of logic, which draws it together with epistemology and metaphysics: Logic, scientific reasoning, is based on definitions, and definitions, correctly formed, correspond to real kinds, not arbitrary sets. Moreover because a science is based on definitions, sciences can be classified according to the types of definition they use, which in turn is based on kind and level of abstraction from matter that they employ, which is all just to say, the way they consider being.

Definitions are clearly important therefore in science. An ideal definition is one that articulates the essence of the thing to be defined. It is structured by takeing the genus and adding to it a differentia which singles the species to be defined out from the rest of the genus, thus, e.g., the species man is defined as a rational (difference) animal (genus), because according to Aquians the essential difference between men and beasts is reason. Again, animal is defined as sensate living-thing.

Aquinas inherited the ten categories from Aristotle, which were meant to be the ten most general genera of being, that is, the ten most generic kinds of things that can be said to be. The most important of these are substance, quality, quantity, and relation (although Aquinas only considers some relations real and not mental).