[Footnote 49: Theophrastus wrote a treatise in three books on the solution of the puzzle called [Greek: O( pseudo/menos] (see the list of his lost works in Diogenes L. v. 49). We find also other treatises entitled [Greek: Megariko\s a/] (which Diogenes cites, vi. 22),--[Greek: A)gônistiko\n tê=s peri\ tou\s e)ristikou\s lo/gous theôri/as--Sophisma/tôn a/, b]--besides several more titles relating to dialectics, and bearing upon the solution of syllogistic problems. Chrysippus also, in the ensuing century, wrote a treatise in three books, [Greek: Peri\ tê=s tou= pseudome/non lu/seôs] (Diog. vii. 107). Such facts show the importance of these problems in their bearing upon logical theory, as conceived by the ancient world. Epikurus also wrote against the [Greek: Megarikoi/] (Diog. x. 27). The discussion of sophisms, or logical difficulties ([Greek: lu/seis a)pori/ôn]), was a favourite occupation at the banquets of philosophers at Athens, on or about 100 B.C. [Greek: A)nti/patros d' o( philo/sophos, sumpo/sio/n pote suna/gôn, sune/taxe toi=s e)rchome/nois ô(s peri\ sophisma/tôn e(rou=sin] (Athenæus, v. 186 C). Plutarch, Non posse suaviter vivi secundum Epicurum, p. 1096 C; De Sanitate Præcepta, c. 20, p. 133 B.] [Footnote 50: Various portions of the Theætêtus illustrate this Megaric sophism (pp. 165-188). The situation assumed in the question of Eubulidês--having before your eyes a person veiled--might form a suitable addition to the various contingencies specified in Theætêt. pp. 192-193. The manner in which the Platonic Sokrates proves (Theæt. 165) that you at the same time see, and do not see, an object before you, is quite as sophistical as the way in which Eubulidês proves that you both know, and do not know, your father.] [Side-note: Causes of error constant--the Megarics were sentinals against them.] The causes of error and fallacy are inherent in the complication of nature, the imperfection of language, the small range of facts which we know, the indefinite varieties of comparison possible among those facts, and the diverse or opposite predispositions, intellectual as well as emotional, of individual minds. They are not fabricated by those who first draw attention to them.[51] The Megarics, far from being themselves deceivers, served as sentinels against deceit. They planted conspicuous beacons upon some of the sunken rocks whereon unwary reasoners were likely to be wrecked. When the general type of a fallacy is illustrated by a particular case in which the conclusion is manifestly untrue, the like fallacy is rendered less operative for the future.