Philosophical Background to Modern Philosophy:
An Introduction for Undergraduates

Contact: Dr. Jan Garrett

Last modified January 26, 2004


I. Conceptual Background
     A. Aristotle's Categories
     B. Substance
     C. Essence and Knowledge
     D. Accident
     E. Property
     F. The Four Causes
     G. Nature
     H. The Significance of Final Cause
     I. The Attack on Final Causes in Natural Philosophy
     J. Descartes' Transformation of Essence

II. Epochs in the History of Philosophy
     A. Ancient (omitted)
     B. Medieval
     C. Modern

I. Conceptual Background

The biggest philosophical influence in Western Europe in the period prior to Descartes is the Christianized version of Aristotelianism taught by the medieval Scholastics, the most important of whom was Thomas Aquinas. We cannot understand modern philosophers, such as Descartes among the rationalists or Locke among the empiricists, unless we understand them as breaking away from, while subtly remaining indebted to, the Aristotelianism of their predecessors and contemporaries.

The most important part of Aristotelianism in this period is Aristotelian metaphysics, not for instance, ethics. Aristotelian physics is important (and I'll have something to say about that soon) but this relationship is less problematic, because the break between the early moderns and the Aristotelians in physics is easier to see. The moderns align themselves with Copernicus and Galileo, with what was then generally called the new science, and are, when they dare, open critics of Aristotelian science.

Aristotle's Categories

The categories are the ten basic classifications of beings according to Aristotle in a little and probably early work known as the Categories. They are:

and two others of minimal importance even to Aristotle. For Aristotle, any item that falls under any of these categories is a being, and one kind of category cannot be reduced to another.


Yet, for all that one of the categories, substance, is most basic. Without substance there could never be qualities, quantities, relations, etc.

In Aristotle's Categories substance has two meanings, but one meaning is primary.

Primary substances are individuals (e.g., this horse, Dobbin, or this human, Socrates).
Aristotle thinks of primary substances as unified beings (the most obvious of which we can point to) and as lasting, at least a while.
Secondary substances are the species and the genera to which primary substances belong because of their essential features.
Human is the species to which Socrates belongs because, say, of being a rational animal. Animal is the genus to which the species human belongs. Genera (plural of genus) collect species on the basis of their shared essential features. Thus, dog and horse belong to animal on the basis of their sharing the power of perception.

Of course, there would be no secondary substances without primary substances.

With this background we can introduce a few metaphysical concepts found first in Aristotle's Topics, essence, accident, and property.

Essence and Knowledge

The Latin term "essentia" translates a Greek phrase that seems awkward even in Greek, but the idea is that there is some phrase and some set of concepts that captures the nature of a thing as it is in itself. The essence of a thing is its true being or nature, and its nature, according to the Aristotelian tradition is knowable.

The Latin term for knowledge is "scientia," from which we get the word "science." Scientia is expressed partly in true definitions, definitions that state in words the essences of things.

For Aristotelians knowledge, however, is not primarily of the individual in its uniqueness or peculiarity but of the universal, the specific nature. Essence comes to be associated with the specific nature of a thing.

Now, the Aristotelians generally thought that the essence of humans was rationality. They explained that the capacity of perception shared with animals was a prerequisite for rationality and having a living body is a prerequisite for perception. So they were able to do justice to the importance of perception and embodiment for rationality.


By contrast with a thing's essence, which is necessarily connected with it, there are accidents. Accidents are roughly correlated with categories other than substances. Socrates may be tan or pale (Tan and Pale are qualities), to the left or the right of Plato (Left of and Right of are relations), speaking or walking (actions), 150# or 155# (quantities), but he does not have to retain any one of these things to retain his human essence.

Accidents are inessential things that never occur by themselves but are "present in" a primary substance. Accidents thus seem metaphysically dependent upon primary substances, but not in the same way that secondary substances are dependent upon primary substances.

Property (of a Thing)

The third important term introduced by Aristotle's Topics is property. A property is correlated with the essence of a thing and is not contingently attached to it as an accident might be.

A property is an aspect a thing must have because of what the thing is essentially-the property depends upon the essence but the property is not the essence.
Someone who knows the properties of things is in an intellectual position superior to someone who merely is aware of their accidents, but someone who knows the essence of things is in a superior position to someone who merely knows their properties. Compared with knowing properties, knowing essence is to know from the inside. It is like knowing why somebody did something (knowing the beliefs and desires behind his action) rather than only knowing that he acted in one way rather than another. Knowing the essence of something, e.g., a right angle triangle, enables one to deduce or demonstrate its properties (e.g., that the square of the hypotenuse is equal to the sum of the square of the two other sides).

The Four Causes or Explanatory Factors

Aristotle's Categories gives us a very incomplete metaphysical system. To go farther he had to introduce other ideas, the most important of which are probably his four causes or explanatory factors. We can use these to take what the Categories consider primary substances, such as Socrates the human being, and analyze them further.

material cause-that out which a thing comes to be and which persists (brass in the key)

formal cause-the whatness or essence of a thing, its shape or pattern (the shape of the key)

efficient cause-the cause of change or rest (the key maker, or the art of the key-maker)

final cause-that for the sake of which, the end or goal (opening locks)

Since individual things, what Aristotle in the Categories calls primary substances, almost always have at least two types of cause (matter and form) and frequently have all four, the question naturally arises as to whether any of these depend on others and may be explained in terms of the others. If you emphasize material cause, you move towards materialism. If you emphasize formal cause, you move toward idealism or Platonism.

The Term "Nature"

The word "nature" is ambiguous and can refer to material, formal, or final causes of a thing. It can also refer to the efficient cause of the movement of a living thing when the thing is moved by its soul, an internal cause.

In his biology, Aristotle tended to link the formal, efficient, and final causes together and contrast them with the material cause. In some later writings, the true substance is not the concrete individual (the primary substance of the categories) but the form of the concrete individual, the soul of the human or animal or plant. Soul in this sense is individual but the same from one member of a species to another. Thus, it is scientifically knowable.

The Significance of Final Causes
for Premodern (Western) Philosophy

Final cause is important for most ancient and medieval philosophies beginning with Plato, whether or not it is referred to as such. Plato's Form of the Good is a final cause in the Republic. The one non-Skeptical school to try to do without the idea of final causes in nature is the atomist (Epicurus is quite conscious of rejecting final causes).

In Aristotle's Nicomachean Ethics, eudaimonia, or happiness, is the final cause of human life in general. Since most humans are not happy, it follows that human beings can exist without fulfilling their final cause. Yet, there is a close connection between form and final cause, at least in living beings.

"Become what you are" is an Arisotelian slogan. On the face of it, it is nonsense, but in Aristotelian terms in makes sense.

This slogan means: perfect yourself as what you are essentially capable of being, i.e., what you can become given what kind of being you are. Human beings are rational animals, that is, they have the rational capacity (perhaps completely untrained or only partly developed). But they can live a flourishing life if they develop this capacity and use it when it is developed. That is why happiness for Aristotle is a life in accordance with virtue (since virtues are developed habits that conform to reason).

Premoderns could also speak of nonhuman living beings becoming what they are, plants growing from seeds to the flowering or reproducing stages; animals growing from cubs or kittens to active adults able to fend for themselves and reproduce. Even the material elements, earth and fire, had final causes; earth tends toward the center of the universe, fire toward the higher elevations.

The Attack on Final Causes in Natural Philosophy

Early modern thought is generally characterized by skepticism about, or outright rejection of, final causes in natural philosophy. Where early moderns like Descartes admit the meaningfulness of the notion, they tend to deny that final causes of material things can be known. This is perhaps the clearest expression of their anti-Aristotelianism. Of course, modern philosophers still speak of goals or purposes, and for awhile permit themselves to talk about God's purposes with respect to the human mind, but increasingly they limit purposes and goals to ones voluntarily adopted by human beings. (Spinoza is more radical than the other seventeenth-century rationalists in this respect: while in Meditation IV Descartes reasons teleologically about the human mind, which for him is nothing physical, Spinoza attacks the notion of final causes in general.)

If you reject final causes as either unintelligible or unknowable but wish to retain the metaphysics of substance and essence, you will have to give up the idea of becoming what one already essentially is. Thus the essence of a thing no longer can be related to what it is somehow "ordered" by nature to become, but must be understood entirely in terms of a feature the thing always and necessarily has, a feature or set of features it cannot be without.

Descartes' Transformation of Essence

Thus, as we shall see, Descartes retains the notion of substance and essence, but essence no longer refers in part to what a being is when it is a perfect specimen of its type. It refers to necessary and sufficient conditions for being a specimen of its type. Thus, for Descartes, the essence of a mental substance is thought. Whatever thinks is a mind, and all minds think. A fairly simple thought (feeling pleasure or pain, for instance, or seeing a red patch) is enough. For Descartes, the essence of a material substance is extension. Whatever occupies space in such a way as to exclude other things like itself is a body, and all bodies occupy space in such a way, etc.

II. Epochs in Philosophy

A. Details about Ancient Philosophy are omitted.

B. Medieval Philosophy

* Is generally similar to ancient philosophy in that the philosophy of value (ethics, theology) dovetails with, and hangs together with, natural philosophy and metaphysics.

* Differs from ancient philosophy and modern philosophy in that theological issues provide the main motivation for the major portion of philosophical inquiry. Medieval philosophers are first of all Christians, Muslims, or Jews, and then philosophers.

They studied

1) the ways of knowledge, including how we come to know God
2) the relations between reason and faith; understanding and Biblical/clerical authority
3) the problem of evil: how is the existence of evil compatible with that of an omnipotent, perfect God
4) the problem of free will and divine foreknowledge: if God foreknows everything that will happen, how can I be free?
5) the relation of body and soul: the nature of personhood is studied for its bearing on the question of immortality
Medieval philosophy is characterized primarily by the doctrine of levels of being. This philosophical commitment is most thoroughly worked out by Thomas Aquinas and his followers, known in various periods as scholastics, schoomen, and nowadays as Thomists.

1) Reality is characterized by a hierarchy of levels, the lowest being mere matter (or possibly "nothingness" = evil), the highest being God.

2) Lower levels are subservient to the higher levels; higher levels have authority over lower levels.

3) Composite beings (creatures with both soul and body) exist on multiple levels, the highest level being the end to which the lower levels are subordinate.

4) Soul-aspects are essentially three

a. vegetative/nutritive: lowest, just above matter, common to all living creatures

b. animal/sensitive: above nutritive, common to all animals, including power of perception

c. rational-above animal, common to human beings, includes power to grasp universals and, with sufficient faith, to "see God."

5) The universe is multi-level, created by God and supported in existence by God for His reasons. Final causes, or natural purposes, are built into the nature of things. The body should serve the soul; the vegetative and animal aspects of the human soul should serve the rational aspect; man should serve God.

6) Faith precedes and makes the way for understanding. Two slogans that express this are: fides quaerens intellectum (faith seeking understanding) and Credo ut intelligam (I believe that I may understand). Faith stretches the soul in such a way that it can mirror more adequately the objects of knowledge that exist at higher levels (i.e., in the mind of God).

C. Modern Philosophy (at least through Kant)

Characterized by the disintegration of the systematic view of reality and value common in the medieval period and various attempts to create new systems.

1. Skepticism about human ability to know God's purposes leads to rejection of the search for the final causes of natural things.

2. The organic view of reality is gradually replaced by one in which Nature at least is regarded as a complex machine: The multiplicity of sensitive and nutritive functions is replaced by the mathematical precision of machinelike systems, which can be measured, manufactured, predicted and controlled.

3. Nature is redefined in terms of mathematizable continua (plural of continuum), i.e., absolute space and time, mass, motion, etc. Emphasis on quality gives way to an emphasis on a quantifiable field.

4) Scientific knowledge (natural philosophy) is radically separated first from ethics and eventually from theology. Often ethical knowledge is denied (reduced to self-interest or personal preference) or ethical judgments are regarded as mere products of convention, i.e., agreements between competing individuals. This leads to the prominence of social contract theory in political philosophy. Societies are often considered less real than individuals. Individual rights are often taken as ethically primary, while duties are regarded as derivative.

5) There is a radical rejection of traditional authorities, "idols" and "anticipations" (Bacon), "prejudgments" (Descartes), "received opinions," and what might earlier have been taken on faith is subject to radical doubt. In its place we find an appeal to pure reason, clear and distinct ideas, "the light of nature," and, with empiricists like Locke, direct sense experience. This is probably the most characteristic feature of what was called the Enlightenment as an intellectual movement.