Stoicism

13. Criteria of truth

To identify the ‘criterion (or criteria) of truth’ was a standard requirement of Hellenistic philosophers (see Hellenistic philosophy). The Greek word kritērion is literally a ‘discriminator’, and a common equivalent was kanōn, ‘yardstick’. A criterion of truth was expected to be something naturally available to every mature human being as a basis for distinguishing true from false. Since it was that which made progress towards philosophical understanding possible, its availability and use could not be restricted to those who were already philosophers. When it came to naming the criterion of truth, the Stoics differed among themselves, but in some form or other they all identified it primarily with the ‘cognitive impression’ (see §12), the concept on which the Academic attack on the criterion likewise focused.

A second criterion, widely used in Stoicism and formally named as a criterion at least by Chrysippus, was prolēpsis, inadequately translated as ‘preconception’. A prolēpsis, literally ‘prior grasp’, is any naturally acquired generic ‘conception’ (ennoia) of a thing (see Prolēpsis). Two other terms which are in most contexts interchangeable with it are koinē ennoia, ‘common conception’ (that is, common to all human beings) and physikē ennoia, ‘natural conception’. These descriptions distinguish prolēpsis from artificially acquired conceptions, usually culture-dependent ones, most of which are not directly given in experience but depend on a synthetic mental process. A centaur, for example, is arrived at by combining natural conceptions, a giant by enlarging them, and so on. Some artificial conceptions are liable to be misleading, but others are an integral part of scientific understanding, for example, one’s conception of the centre of the earth, acquired ‘by analogy with smaller spheres’. Human reason is itself simply an ample stock of conceptions, some but not all of them natural ones.

What makes a prolēpsis a reliable guide to truth is precisely the fact that the natural conception has not been tampered with. But where does the prolēpsis itself come from? The Stoics sometimes sound like hard-line empiricists, as when they compare the mind of a new-born infant to a blank sheet of paper which will in due course have its stock of natural conceptions written on it by repeated sense impressions, classified and stored as ‘experience’. Here a prolēpsis is ‘natural’ in the sense of being mechanically imprinted on us, and hence unmediated by fallible reasoning. However, some texts indicate that at least basic moral notions are called natural for the quite different reason that they are dispositionally innate in us.

Many Stoic arguments proceeded from appeals to some prolēpsis or ‘common conception’. This was their version of the widespread philosophical practice of citing what are alleged to be ‘our intuitions’. It ran into the difficulty that such a practice always faces: separating genuinely natural conceptions from those infected by one’s culture or other beliefs becomes the new bone of contention. For example, both Stoics and Epicureans appealed to the prolēpsis of ‘god’, but while the Stoics regarded providence as an integral part of this prolēpsis, the Epicureans argued that god’s providentiality was a cultural imposition on the basic prolēpsis, motivated by human bafflement at the world’s workings (see Epicureanism §9). A very similar dispute launches Stoic ethics.