The doctrine is contradicted (continues Sokrates) by the common opinions of mankind: for no man esteems himself a measure on all things. Every one believes that there are some things on which he is wiser than his neighbour--and others on which his neighbour is wiser than he. People are constantly on the look out for teachers and guides.[50] If Protagoras advances an opinion which others declare to be false, he must, since he admits their opinion to be true, admit his own opinion to be false.[51] No animal, nor any common man, is a measure; but only those men, who have gone through special study and instruction in the matter upon which they pronounce.[52] [Footnote 50: Plato, Theætêt. p. 170.] [Footnote 51: Plato, Theætêt. p. 171 B. [Greek: Ou)kou=n tê\n au(tou= a)\n pseudê= xugchôroi=, ei) tê\n tô=n ê(goume/nôn au)to\n pseu/desthai o(mologei= a)lêthê= ei)=nai?]] [Footnote 52: Plato, Theætêt. p. 171 C.] [Side-note: In matters of present sentiment every man can judge for himself. Where future consequences are involved special knowledge is required.] In matters of present and immediate sensation, hot, cold, dry, moist, sweet, bitter, &c., Sokrates acknowledges that every man must judge _for himself_, and that what each pronounces is true _for himself_. So too, about honourable or base, just or unjust, holy or unholy--whatever rules any city may lay down, are true _for itself_: no man, no city,--is wiser upon these matters than any other.[53] But in regard to what is good, profitable, advantageous, healthy, &c., the like cannot be conceded. Here (says Sokrates) one man, and one city, is decidedly wiser, and judges more truly, than another. We cannot say that the judgment of each is true;[54] or that what every man or every city anticipates to promise good or profit, will necessarily realise such anticipations. In such cases, not merely present sentiment, but future consequences are involved. [Footnote 53: Plato, Theætêt. pp. 172 A, 177 E.] [Footnote 54: Plato, Theætêt. p. 172.] Here then we discover the distinction which Plato would draw.[55] Where present sentiment alone is involved, as in hot and cold, sweet and bitter, just and unjust, honourable and base, &c., there each is a judge for himself, and one man is no better judge than another. But where future consequences are to be predicted, the ignorant man is incapable: none but the professional Expert, or the prophet,[56] is competent to declare the truth. When a dinner is on table, each man among the guests can judge whether it is good: but while it is being prepared, none but the cook can judge whether it _will be_ good.[57] This is one Platonic objection against the opinion of Protagoras, when he says that every opinion of every man is true. Another objection is, that opinions of different men are opposite and contradictory,[58] some of them contradicting the Protagorean dictum itself. [Footnote 55: Plato, Theætêt. p. 178.]