[Footnote 90: Analyt. Post. I. xxxii. p. 88, a. 18-b. 29. [Greek: ai( ga\r a)rchai\ dittai/, e)x ô(=n te kai\ peri\ o(\; ai( me\n ou)=n e)x ô(=n koinai/, ai( de\ peri\ o(/ i)/diai, oi(=on a)rithmo/s, me/gethos.] Compare xi. p. 77, a. 27. See Barthélemy St. Hilaire, Plan Général des Derniers Analytiques, p. lxxxi.] Science or scientific Cognition differs from true Opinion, and the _cognitum_ from the _opinatum_, herein, that Science is of the Universal, and through necessary premisses which cannot be otherwise; while Opinion relates to matters true, yet which at the same time may possibly be false. The belief in a proposition which is immediate (_i. e._, undemonstrable) yet not necessary, is Opinion; it is not Science, nor is it Noûs or Intellect--the _principium_ of Science or scientific Cognition. Such beliefs are fluctuating, as we see every day; we all distinguish them from other beliefs, which we cannot conceive not to be true and which we call cognitions.[91] But may there not be Opinion and Cognition respecting the same matters? There may be (says Aristotle) in different men, or in the same man at different times; but not in the same man at the same time. There may also be, respecting the same matter, true opinion in one man's mind, and false opinion in the mind of another.[92] [Footnote 91: Analyt. Post. I. xxxiii. p. 88, b. 30-p. 89, a. 10.] [Footnote 92: Ibid. p. 89, a. 11-b. 6. That eclipse of the sun is caused by the interposition of the moon was to the astronomer Hipparchos scientific Cognition; for he saw that it _could not_ be otherwise. To the philosopher Epikurus it was Opinion; for he thought that it _might_ be otherwise (Themistius, p. 66, Spengel).] With some remarks upon Sagacity, or the power of divining a middle term in a time too short for reflection (as when the friendship of two men is on the instant referred to the fact of their having a common enemy), the present book is brought to a close.[93] [Footnote 93: Ibid. xxxiv. p. 89, b. 10-20.] CHAPTER VIII. ANALYTICA POSTERIORA II. Aristotle begins the Second Book of the Analytica Posteriora by an enumeration and classification of Problems or Questions suitable for investigation. The matters knowable by us may be distributed into four classes:-- [Greek: O(/ti]. [Greek: Dio/ti]. [Greek: Ei) e)/sti]. [Greek: Ti/ e)sti]. 1. Quod. 2. Cur. 3. An sit. 4. Quid sit.