OPINION (Lat. opinio, from opinari, to think), a term used loosely in ordinary speech for an idea or an explanation of facts which is regarded as being based on evidence which is good but not conclusive. In logic it is used as a translation of Gr. 66^a, which plays a prominent part in Greek philosophy as the opposite of knowledge (iwiarr^fxT] or aKrid(ia). The distinction is drawn by Parmenides, who contrasts the Sphere of truth or knowledge with that of opinion, which deals with mere appearance, error, not-being. So Plato places 56^a between aicrdr)(ns and Siai'ota, as dealing with phenomena contrasted with non-being and being respectively. Thus Plato confines opinion to that which is subject to change. Aristotle, retaining the same idea, assigns to opinion (especially in the Ethics) the Sphere of things contingent, i.e. the future: hence opinion deals with that which is probable. More generally he uses jjopulur opinion - that which is generally held to be true (8oKttv) - as the starting-point of an inquiry. In modern philosophy the term has been used for various conceptions all having much the same connotation. The absence of any universally acknowledged definition, especially such as would contrast " opinion " with " belief," " faith " and the like, deprives it of any status as a philosophic term.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)