But in the case of Herodotus it will be more instructive to pass on from points like these to those questions of general probability, the true apprehension of which depends rather on a certain quality of mind than on any possibility of formulated rules, questions which form no unimportant part of scientific history; for it must be remembered always that the canons of historical criticism are essentially different from those of judicial evidence, for they cannot, like the latter, be made plain to every ordinary mind, but appeal to a certain historical faculty founded on the experience of life. Besides, the rules for the reception of evidence in courts of law are purely stationary, while the science of historical probability is essentially progressive, and changes with the advancing spirit of each age. Now, of all the speculative canons of historical criticism, none is more important than that which rests on psychological probability. Arguing from his knowledge of human nature, Herodotus rejects the presence of Helen within the walls of Troy. Had she been there, he says, Priam and his kinsmen would never have been so mad (_φρενοβλαβεῖς_) as not to give her up, when they and their children and their city were in such peril (ii. 118); and as regards the authority of Homer, some incidental passages in his poem show that he knew of Helen’s sojourn in Egypt during the siege, but selected the other story as being a more suitable motive for an epic. Similarly he does not believe that the Alcmæonidæ family, a family who had always been the haters of tyranny (_μισοτύραννοι_), and to whom, even more than to Harmodios and Aristogeiton, Athens owed its liberty, would ever have been so treacherous as to hold up a shield after the battle of Marathon as a signal for the Persian host to fall on the city. A shield, he acknowledges, was held up, but it could not possibly have been done by such friends of liberty as the house of Alcmæon; nor will he believe that a great king like Rhampsinitus would have sent his daughter _κατίσαι ἐπ’ οἰκήματος_. Elsewhere he argues from more general considerations of probability; a Greek courtesan like Rhodopis would hardly have been rich enough to build a pyramid, and, besides, on chronological grounds the story is impossible (ii. 134). In another passage (ii. 63), after giving an account of the forcible entry of the priests of Ares into the chapel of the god’s mother, which seems to have been a sort of religious faction fight where sticks were freely used (_μάχη ξύλοισι καρτερή_), ‘I feel sure,’ he says, ‘that many of them died from getting their heads broken, notwithstanding the assertions of the Egyptian priests to the contrary.’ There is also something charmingly naïve in the account he gives of the celebrated Greek swimmer who dived a distance of eighty stadia to give his countrymen warning of the Persian advance. ‘If, however,’ he says, ‘I may offer an opinion on the subject, I would say that he came in a boat.’