Let's differentiate between types of knowledge-opinion (and fact-opinion) distinctions. On the one hand, such distinctions can be drawn in a way that is topic-neutral; in which case, there is nothing in the proposition in question that determines whether it can be known or merely opined. A proposition that is opined on one occasion can, in other cases, be known, and what determines whether it is known or merely opined will be the amount of evidence in its favour. On the other hand, a knowledge-opinion distinction can be topic-based; in which case, the content of the knowledge or opinion determines whether it can be known or merely opined; that is, the nature of the proposition determines which of the two categories it can fall into. For example, recent fact-opinion distinctions tend to relegate value-judgments to the category of opinion simply because they concern values.
The medieval knowledge-opinion distinction was topic-based. Only universal, necessarily true statements were candidates for knowledge. Contingent propositions could, at best, be opined but not known. This topic-based distinction appeared in several English-language texts in the 16th and 17th centuries. Examples follow. (I've reproduced here two quotations from the previous post this series in order to gather these examples all in one place.)
First, we have Abraham Fraunce's The Lawyer's Logic (1588), according to which, 'Artificial logic then is the polishing of natural wit, as discovering the validity of every reason, be it necessary, whereof cometh Science: or contingent, whence proceedeth opinion' (Fraunce, The Lawyer's Logic [1588], p. ???).
Next, from Blundeville's Art of Logike (1599) there is this proclamation:
All these intellectual habits are contained under a certain and most sure knowledge, which is always true, for uncertain knowledge is sometimes true, and sometimes false: whereto belongeth opinion, suspicion, conjecture, and such like. (Thomas Blundeville, The Art of Logike [1599], p. 28)The next example is from a text (Elementa logica, 1598) that was first published in Latin and then translated by the author into French. The author is Pierre Du Moulin. His text was very popular in Europe and went through 40 editions. It was translated into English by Nathanael De Lawne in 1624. According to Du Moulin,
To have the science of a thing, two certainties are required. The one is, that the thing be certain of itself and unchangeable. The second is, that the persuasion which we have of it be firm and clear. If either of these two certainties be wanting it is no Science, but opinion. ... Science is a certain knowledge of a certain thing by the next cause. Opinion is a doubtful or false knowledge. Faith is a firm persuasion grounded upon the testimony of some other. If a man know certainly a thing because he seeth it, or toucheth it, that is neither called Science, nor Faith, nor opinion; but sense, which knoweth only things singular : but Science is of things universal. (Du Moulin, Elements of Logick [1624], pp. 162-3)Thomas Spencer's Art of Logick (1628) has this passage:
A true axiom is ... Contingent, when it is in such sort true, that it may also at sometime be false. This is called opinion' (pp. 156-7).... Illations being pronounced by God, have always a necessary verity .... [B]ut these propositions being pronounced by man, do contain (at the best) but opinion, contingent, and conjecture all knowledge. (Spencer, The Art of Logick [1628], p. 232)In his Art of Logick(1654), Zachary Coke distinguished between contingent and necessary syllogisms, adding that 'a Contingent ... getteth a suspended and weak assent to the conclusion, and is called opinion' (Coke, Art of Logick [1654], p. 157, italics in original).
Finally, we have this selection from Robert Burthogge's Discourse of Reason and Truth (1678):
Firm Assent in matters in themselves mutable and of a contingent nature, may be called Confidence: but in matters of a necessary, firm, and immutable nature, it is Science. Infirm Assent, or Assent with Dubitation, is called Opinion. Suspicion is a beginning Assent, or an inclination to believe a thing, and is short of Opinion. Suspicion on grounds is called just suspicion. Suspicion on no grounds is mere suspicion. Probability is appearance of Truth : And ground of Suspicion is Appearance of Probability. (Organum Vetus &Novum or, a Discourse of Reason and Truth [1678], p. 47)Lyrics NSFW.