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 and foresees that in consequence he will not be able to attend Mass on the following day, is the sin of omitting to hear Mass committed on the Saturday night, when he voluntarily posits the cause of his not hearing Mass on the following day, or on the Sunday, when Mass is not heard as is of obligation? Inasmuch as a formal sin is a human act, it would seem that we must say with St Alphonsus that the sin is committed when the cause of the omission or of the evil is voluntarily posited, otherwise we should have to say that a man may commit sin without knowing it, or while he is asleep.