The history of the higher forms of ancestor-worship in other countries would lead us to suppose that the public ceremonies of the Shinto-cult must include some rite of purification. As a matter of fact, the most important of all Shinto ceremonies is the ceremony of purification,--o-harai, as it is called, which term signifies the casting-out or expulsion of evils .... In ancient Athens a corresponding ceremony took place every year; in Rome, every four years. The o-harai is performed twice every year,--in the sixth month and the twelfth month by the ancient calendar. It used to be not less obligatory than the Roman lustration; and the idea behind the obligation was the same as that which inspired the Roman laws on the subject .... So long as men believe that the welfare of the living depends upon the will of the dead,--that all happenings in the world are ordered by spirits of different characters, evil as well as good,--that every bad action lends additional power to the viewless [145] forces of destruction, and therefore endangers the public prosperity,--so long will the necessity of a public purification remain an article of common faith. The presence in any community of even one person who has offended the gods, consciously or unwillingly, is a public misfortune, a public peril. Yet it is not possible for all men to live so well as never to vex the gods by thought, word, or deed,--through passion or ignorance or carelessness. "Every one," declares Hirata, "is certain to commit accidental offences, however careful he may be... Evil acts and words are of two kinds: those of which we are conscious, and those of which we are not conscious .... It is better to assume that we have committed such unconscious offences." Now it should be remembered that for the man of Old Japan,--as for the Greek or the Roman citizen of early times,--religion consisted chiefly in the exact observance of multitudinous custom; and that it was therefore difficult to know whether, in performing the duties of the several cults, one had not inadvertently displeased the Unseen. As a means of maintaining and assuring the religious purity of the people periodical lustration was consequently deemed indispensable.