The first point to notice is that these rites were applicable only to _involuntary_ acts of commission or omission—an offence against the gods (nefas) if wittingly committed, was inexpiable. In this case the offender was _impius_, i. e. had wilfully failed in his duty; and him no rites could absolve[1334]. But by ordinary offences against the gods we are not to understand _sin_, in the Christian sense of the word; they were rather mistakes in ritual, or involuntary omissions—in fact any real or supposed or possible errors in any of a man’s relations to the _numina_ around him. He might always be putting himself in the wrong in regard to these relations, and he must as sedulously endeavour to right himself. In the life of the ‘privatus’ these trespasses in sacred law would chiefly be in matters of marriages and funerals and the regular sacrifices of the household; in the life of the magistrate they would be mistakes or omissions in his duties on behalf of the State[1335]. Whether in private or public life, they must be duly expiated. It is needless to point out how powerful a factor this belief must have been in the growth of a conscience and of the sense of duty; or how stringent a ‘religio’ was that which, assuming that a man could hardly commit an offence except unwittingly, made the possible exceptional case fatal to his position as a member of a community which depended for its wholesome existence on the good will of the gods. Remembering that among the divine beings to whom it was most essential for each family to fulfil its duties, were the _di manes_, or dead ancestors and members of the family, we see at once that February with its Parentalia was an important month in the matter of expiatory rites. Ovid, though suggesting a fancy derivation for the name of the month, expresses this idea clearly enough: Aut quia _placatis_ sunt tempora pura sepulcris Tum cum ferales praeteriere dies[1336]. But the other etymology given by the poet is, as we have seen, the right one, and may bring us to another class of _piacula_, of which we find an example this month in the Lupercalia. Mensis ab his dictus, secta quia pelle Luperci Omne solum lustrant, idque piamen habent[1337].