'Doxa' in Ancient Greek philosophy refers to common belief or popular opinion, which contrasts with 'episteme', signifying true and justifiable knowledge. This distinction is mirrored in contemporary discussions where doxa is akin to the modern understanding of opinion—views held by individuals or society that are not necessarily substantiated by evidence or rigorous rationality. In contemporary terms, opinion, akin to doxa, lacks the robust justificatory framework that characterises knowledge (episteme). The juxtaposition of doxa with episteme has laid the groundwork for understanding the transformation of opinion into knowledge through the addition of truth and justification.

The Gettier problem presents scenarios where an individual has a belief that is true and justified, yet intuitively, these scenarios do not seem to result in actual knowledge. This challenges the traditional tripartite definition of knowledge by suggesting that there could be instances of justified true belief that do not constitute knowledge—indicating that another component or condition might be necessary for a true belief to be considered knowledge. Essentially, the Gettier problem demonstrates that the criteria of truth, belief, and justification may be necessary for knowledge, but they are not always sufficient, as they do not account for the role of luck or error in the formation of a belief.

An opinion can indeed be wrong when it conflicts with established facts or more substantiated beliefs. The wrongness of an opinion does not alter its status as an opinion because opinions are inherently subjective and personal. They are often expressions of individual feelings, tastes, or preferences, which do not require grounding in truth. However, an opinion that purports to make factual claims can be challenged and discredited if those claims are demonstrably false. The merit of an opinion is often gauged by its reasonableness and coherence with known facts, but its correctness is not a criterion for its status as an opinion.

It is generally accepted in philosophical terms that belief is a necessary component of knowledge. To know something, one must also believe it; if one claims to know something but does not believe it, this is considered a contradiction. Belief is the psychological state of holding a proposition to be true. Without the commitment of belief, the certainty required for knowledge is absent. Knowledge without belief would imply an absence of personal conviction, reducing knowledge to a mere external artifact devoid of a knower’s cognitive assent. Therefore, belief is integral to knowledge as it signifies the internal acceptance and endorsement of a truth claim.

The concept of 'consensus gentium'—the agreement of the many—suggests that when a large number of people hold the same opinion, it gains credibility. However, from an epistemological standpoint, consensus does not necessarily elevate opinion to knowledge. While widespread belief can be a compelling reason to accept an opinion as a provisional truth, it still requires independent justification to be considered knowledge. Moreover, history has shown that consensus can be mistaken, reinforcing that knowledge demands more than mere agreement; it necessitates objective truth and justification that withstands critical scrutiny and empirical testing.