ואם נפש (כי) תחטא בשגגה ולא ידע. לא שנודעה לו אחר כך לא בתחילה ולא בסוף על מה תורה מחייבתו קרבן אלא שידע שעשה מלאכה בשבת ואינו יודע אם מבעוד יום או משחשכה או חתיכה שאכל אם שומן אם חלב וכל כיוצא בזה שמביא אשם תלוי ואם נודע לו ודאי חייב להביא אשם ודאי וכפר עליו על שגגתו אשר שגג שהוא עד עתה בשגגתו, ע"כ מפר"ח. (כ"י מינכען 26 דף 275 ע"ב): ואם נפש כי תחטא וגו'...ולא ידע; this does not mean that the party concerned never became aware of this offence. If that were so, how could the Torah demand a sacrifice from him, etc.? The Torah describes the following scenario: someone had performed an activity which is definitely prohibited on the Sabbath. He does not know if at the hour he had performed this activity the Sabbath had already concluded or not. Or, he entertains a doubt of a different kind, such as having eaten one of two pieces of meat believing it to be kasher. In the meantime he has been made aware that one of the two pieces of meat had not been kasher. He has no means of finding out now which piece he had eaten, i.e. the doubt will forever remain unresolved. In such situations the offering he has to bring is the one known as אשם תלוי, a provisional guilt offering, i.e. pending clarification of what precisely if any his sin had been, this is all he can do in the meantime. Once he finds out that he has indeed committed the sin he was in doubt about, he has to bring (additionally) the regular sin-offering appropriate for the offence in question. וכפר עליו הכהן על שגגתו אשר שגג, which until this time had been an inadvertent sin.