OPINION. - An assertion to which assent is given, but evidence (v.) of its truth.
Parmenide identifies opinion (δῶς) with sensible knowledge and devalues it (H. Diels, Die Fragm. d. Vorsokratiker, 4th ed., Berlino 1922; fr. 8, lin. 30 sgg.). The Sophists hold that it is the only possible knowledge, while recognizing it to be changeable and unstable (Regia, op. cit. in bibl., p. 24 sgg.). For Platone, o. is an imperfect knowledge midway between ignorance and science (ibid., p. 46), because its object is the world of becoming, which stands between non-being and true being. Aristotele, who attributes greater value to the sensible world, also values o. more highly. In Greek philosophy, science (ἐπιστήμη) is opposed to o.; it is knowledge of the necessary, of that which cannot be otherwise, demonstrated knowledge (Anal. post., I, cap. 2).
O. doubt (v.), since doubt is the suspension of assent, whereas in o. assent is given, albeit with a certain fear that the opposite may be true.