II. THE CLASSICAL VIEW OF KNOWLEDGE
The traditional analysis of knowledge assumes two key terminological conventions. For Plato, these conventions were that:
- The object of “knowledge” must be unalterable.
- It must be possible to make a voluntary judgment about the truth or falsehood of a proposition concerning the object.
These conventions present problems when discussing knowledge of truths derived from sense perception. Plato assumed that sense perception pertains to a Heracleitean flux and is thus both involuntary and indubitable. Because it violates the criteria—by being about the alterable and by compelling involuntary assent—sense perception does not qualify as “knowledge” in Plato’s framework.
The Skeptical View
A similar distinction is maintained by Sextus Empiricus, who contrasts reports of sense phenomena (appearances) with empirical judgments:
“Skepticism is an ability, or mental attitude, which opposes appearances to judgments in any way whatever. . .”
“By ‘appearances’ we now mean the objects of sense-perception, whence we contrast them with the objects of thought or ‘judgments.'”
Sextus identifies characteristics of sense phenomena that exclude them from knowledge:
- Affective sense-impressions induce assent involuntarily, constituting appearances.
- These impressions are not subject to rational questioning, as they are “involuntarily indubitable.”
He writes:
“The criterion, then, of the Skeptic School is, we say, the appearance, giving this name to what is virtually the sense-presentation. For since this lies in feeling and involuntary affection, it is not open to question. Consequently, no one disputes that the underlying object has this or that appearance; the point of dispute is whether the object is in reality such as it appears to be.”
For the Skeptics, cognitions divide into two types:
- Appearances: Cognitions that compel involuntary assent.
- Judgments: Cognitions subject to voluntary assent or dissent.
Knowledge, if it exists, belongs to the domain of voluntary judgments. Knowledge is equated with justified true voluntary judgment or, in Skeptic terminology, “true judgment according to the criterion.” The criterion signifies what justifies rational assent. Since sense perception is involuntary, it falls outside the domain of “knowledge” according to this framework.
The Cartesian View
Descartes preserves this terminological convention. He locates error in those cognitions where voluntary assent, dissent, or suspension of judgment is possible:
“Now as to what concerns ideas, if we consider them only in themselves and do not relate them to anything else beyond themselves, they cannot properly speaking be false. . .”
“If I consider the ideas only as certain modes of my thoughts, without trying to relate them to anything beyond, they could scarcely give me material for error.”
Thus, involuntary perceptions (e.g., sense presentations) are excluded from the domain of “knowledge,” as error pertains only to voluntary judgments.
The Lewisian Perspective
C.I. Lewis also maintains this distinction by avoiding the use of “knowledge” or “judgment” in relation to sense presentations or “the given.”
“Apprehension of the presented quale, being immediate, stands in no need of verification; it is impossible to be mistaken about it. Awareness of it is not judgment in any sense in which judgment may be verified; it is not knowledge in any sense in which ‘knowledge’ connotes the opposite of error.”
To address objections that perceptions of objective facts (e.g., “the object before me is a pink ice cube”) may also seem involuntarily given, a distinction must be made between dubitable and indubitable givens. The argument from illusion—highlighting conditions that cause unveridical perceptions—helps draw this distinction. Indubitable cognition refers to phenomenal appearances, aligning with the Platonic-Skeptical-Cartesian-Lewisian tradition of separating appearances from judgments.
The Evolution of Knowledge
The traditional analysis equates knowledge with justified true belief (voluntary judgment). Using Skeptic terminology, knowledge is defined as “true judgment according to the criterion.” The criterion ensures rational justification for assent, dissent, or suspension of judgment. However, since sense presentations are involuntary, they are excluded from the classical realm of “knowledge.”
Over time, two terminological conventions have evolved:
- The inclusion of empirical knowledge.
- The integration of sense perception into discussions of justified true belief.
This evolution reflects shifts in philosophical perspectives, broadening the scope of what counts as “knowledge.”