Back to basics: The categories (avot) of prohibited labor on Shabbat, their sub-categories (toladot), and the significance of having both avot and toladot. Now, if one forgot that it was shabbat or forgot that the given action violated shabbat... the avot and toladot lead to careful bookkeeping, which minimize the number of sin-offeringa that would be needed. Also, note that this is all the negative aspect of Shabbat (making sure not to violate Shabbat, "shamor"), but don't forget the positive side of things (as found in the mitzvah to remember Shabbat ("zakhor"). Also, a couple of cases where these rules apply, where one truly forgets that it is shabbat. Who's Who: Munbaz.