TRUTH. The concept of truth belongs to the 'fundamental philosophical problems—in fact, one may describe it as the central question of all theoretical philosophy. The first step in philosophic reflection consists in asking the question concerning the nature and criteria of truth. The world of being is no longer accepted as a simple datum, but a "reason" for it is required; a "principle" is sought which will enable human cognition to distinguish "gen uine" being from "non-genuine" being, "reality" from "appear ance," truth from error. The same change of attitude occurs also in regard to values. Here, too, cognition is not satisfied with the values accepted on the testimony of tradition, custom or authority, but inquires into the meaning of the difference between "good" and "evil," and seeks universally valid, "objective" norms to justify this distinction. In this two-fold significance, the prob lem of truth was first raised in Greek philosophy. From it evolved the various fields of philosophy within Greek thought. Logic as also ethics and physics have their common root in the problem of truth. For they are all founded on the presupposition that both the immediate view of reality, as presented to us in perception, and the immediate purposes pursued by instinctive impulse and desire, are not finally valid. This immediacy is transcended in the theoretical as well as in the practical sense : it is "questioned" and "called to account." This account implies that from now on, in the sphere of thinking, as in that of willing, individual contents are distinguished as having positive or negative value, the latter being rejected as "invalid," the former retained as "valid." This fundamental distinction forms the pervading theme of Greek phi losophy.
The individual systems differ only in the means by which they try to solve it, by which they try to obtain a clear definition of the difference between "True" and "False." In theoretical respects, the first step is made when the cer tainty of immediate sense perception is shaken and is opposed by another, "critical" authority. It is not the senses which decide about truth and falsehood, about being and non-being ; the de cision rests with reason, pure thought. The beginnings of this view can be traced to the older Ionian philosophy of nature, but it reached its proper development only in the classical systems of the great pre-Socratics. Parmenides and Heraclitus, Pythagore
anism and Atomism reject unanimously the view of the world as perceived through the senses and oppose to it another view which is based on thought—the power of the "Logos." According to Heraclitus, the senses alone are "bad witnesses": they can be used for a knowledge of reality only when they are judged by the soul as to their value and truth. The senses individualize and separate ; as long as we follow them exclusively, each per ceiving mind has its own world in which it remains enclosed. Thought, however, is "common to all": by means of it, alone, we reach a universally valid, "objective" view of the cosmos. "It is a duty to follow that which is common ; but although the Logos is common to all, the majority live as though they had an insight of their own" (Heraclitus, Fragment 2 [Diels] ; cf. Fragments 72, 89, 112-114). "Wisdom resides in One, in the recognition of the reason which pervades all and everything" (fr. 41). According to Parmenides, the road to truth consists in not allowing oneself to be misled by well-worn habit into trusting sense perception: "no, by reason decide the controversial test, the question of Being and Non-Being" (Parmenides, Fragment I, cf. 33 sqq.). The true power of conviction (rians CAnOils) does not reside in the senses but in pure thought : "for thinking and being are the same." Similarly, the Pythagoreans see the true essence of reality in number, because number is to them the principle of all truth. "For nothing of delusion (keRos) does the nature of number admit ; but delusion occurs only in the realm of the unlimited, the unreasonable, and of that which is not determined by the Logos" (Philolaos, Fragment i 1). Democritus distinguishes two forms of cognition : the genuine and the spurious one. The spurious one comprises sight, hearing, taste, smell and touch—in short, the whole world of sense qualities, which exist only "according to custom";—the genuine one gives us an insight into the veritable, the "true" reality, which belongs only to the atoms and empty space (Democritus, Fragment II).