HISTORICAL OUTLINE


The first efforts of Greek thinkers centre around the study of nature. This early

philosophy is almost exclusively objective, and supposes, without examining it,

the validity of knowledge. Doubt arose later chiefly from the disagreement of

philosophers in determining the primordial elements of matter and in discussing

the nature and attributes of reality. Parmenides holds that it is unchangeable;

Heraclitus, that it is constantly changing; Democritus endows it with an eternal

inherent motion, while Anaxagoras requires an independent and intelligent motor.

This led the Sophists to question the possibility of certitude, and prepared the

way for their sceptical tendencies. With Socrates, Plato, and Aristotle, who

oppose the Sophists, the power of the mind to know truth and reach certitude is

vindicated, and the conditions for the validity of knowledge are examined. But

epistemological questions are not yet treated on their own merits, nor kept

sufficiently distinct from purely logical and metaphysical inquiries. The

philosophy of the Stoics is primarily practical, knowledge being looked upon as a

means of right living and as a condition of happiness. As man must act

according to guiding principles and rational convictions, human action supposes

the possibility of knowledge. Subordinating science to ethics, the Epicureans

admit the necessity of knowledge for conduct. And since Epicurean ethics rests

essentially on the experience of pleasure and pain, these sensations are

ultimately the practical criterion of truth. The conflict of opinions, the impossibility

of demonstrating everything, the relativity of perception, became again the main

arguments of scepticism. Pyrrho claims that the nature of things is unknowable,

and consequently we must abstain from judging; herein consist human virtue and

happiness. The representatives of the Middle Academy also are sceptical,

although in a less radical manner. Thus Arcesilaus, while denying the possibility

of certitude and claiming that the duty of a wise man is to refuse his assent to

any proposition, admits nevertheless that a degree of probability sufficient for the

conduct of life is attainable. Carneades develops the same doctrine and

emphasizes its sceptical aspect. Later sceptics, Ænesidemus, Agrippa, and

Sextus Empiricus, make no essential addition.


The Fathers of the Church are occupied chiefly in defending Christian dogmas,

and thus indirectly in showing the harmony of revealed truth with reason St.

Augustine goes farther than any other in the analysis of knowledge and in the

inquiry concerning its validity. He wrote a special treatise against the sceptics of

the Academy who admitted no certain, but only probable, knowledge. What is

probability, he asks in an argument ad hominem, but a likeness of or an

approach to truth and certitude? And then how can one speak of probability who

does not first admit certitude? On one point at least, the existence of the thinking

subject, doubt is impossible. Should a man doubt everything or be in error, the

very fact of doubting or being deceived implies existence. First logical principles

also are certain. Although the senses are not untrustworthy, perfect knowledge is

intellectual knowledge based on the data of the senses and rising beyond them

to general causes. In medieval philosophy the main epistemological issue is the

objective value of universal ideas. After Plato and Aristotle the Scholastics hold

that there is no science of the individual as such. As science deals with general

principles and laws, to know how far science is legitimate it is necessary to

know first the value of general notions and the relations of the universal to the

individual. Does the universal exist in nature, or is it a purely mental product?

Such was the question raised by Porphyry in his introduction to Aristotle's

"Categories". Up to the end of the twelfth century the answers are limited to two,

corresponding to the two, possibilities mentioned by Porphyry. Hence if one may

speak of Realism at that period, it does not seem altogether correct to speak of

Conceptualism or Nominalism in the well-defined sense which these terms have

since acquired (see De Wulf, Hist. de la phil. médiévale, 2d ed., Louvain 1905).

Later, a distinction is introduced which St. Thomas formulates clearly and which

avoids both extremes. The universal as such does not exist in nature, but only in

the mind. Yet it is not a mere product of mental activity; it has a basis in really

existing things; that is, by their individual and by their common features, existing

things offer to the mind a basis for the exercise of its functions of abstraction and

generalization. This moderate Realism, as it is called in opposition to

Conceptualism on the one side, and on the other, to exaggerated, or absolute

Realism, is also essentially the doctrine of Duns Scotus; and it prevailed in the

School till the period of decadence when Nominalism or Terminism was

introduced by Occam and his followers.


In modern times Descartes may be mentioned for his methodical doubt and his

solution of it in the Cogito, ergo sum, i.e. I think, therefore, I exist. But Locke, in

his "Essay concerning Human Understanding", is the first to give a clear

statement of epistemological problems. To begin with ontological discussions is

to begin "at the wrong end" and to take "a wrong coursed." Hence "it came to my

thoughts that . . . before we set ourselves upon inquiries of that nature, it was

necessary to examine our own abilities, and to see what objects our

understandings were, or were not fitted to deal with" (Epistle to the Reader).

Locke's purpose is to discover "the certainty, evidence and extent" of human

knowledge (I, i, 3), to find "the horizon which sets the bounds between the

enlightened and dark parts of things, between what is, and what is not

comprehensible by us (I, i, 7), and "to search out the bounds between opinion

and knowledge" (I, i, 3). One who reflects on the contradictions among men, and

the assurance with which every man maintains his own opinion "may perhaps

have reason to suspect that either there is no such thing as truth at all, or that

mankind hath no sufficient means to attain a certain knowledge of it" (I, i, 2). This

investigation will prevent us from undertaking the study of things that are "beyond

the reach of our capacities" (I, i, 4), and will be "a cure of skepticism and

idleness" (I, i, 6). Such is the problem; among the main points in its solution may

be mentioned the following: "we have the knowledge of our own existence by

intuition; of the existence of God by demonstration; and of other things by

sensation" (IV, ix, 2). The nature of the soul cannot be known, nor does the

trustworthiness of the senses extend to "secondary qualities"; a fortiori,

substance and essences are unknowable. These and other conclusions,

however, are not reached by a truly epistemological method, i.e. by the criticism

of the processes and postulates of knowledge, but almost exclusively by the

psychological method of mental analysis. Following in Locke's footsteps and

proceeding farther, Berkeley denied the objectivity even of primary qualities of

matter, and Hume held a universal and radical phenomenalism. Aroused from his

"dogmatic slumber" by the skepticism of Hume, Kant took up again the same

problem of the extent, validity, and limits of human knowledge. This is the task of

criticism, not the criticism of books and systems, but of reason itself in the

whole range of its powers, and in regard to its ability to attain knowledge

transcending experience. Briefly stated, the solution reached by Kant is that we

know things-as-they-appear, or phenomena, but not the noumena, or

things-in-themselves. These latter, precisely because they are outside the mind,

are also outside the possibility of knowledge. Kant's successors, identifying the

theory of being with the theory of knowing, elaborated his "Critique" into a

system of metaphysics in which the very existence of things-in-themselves was

denied. After Kant we reach the present period in the evolution of epistemological

problems.