“ One who recites Shema but doesn't make it audible to his ear - has fulfilled his obligation. Rabbi Yosei says: Has not fulfilled his obligation. One who recites but does not articulate each letter: Rabbi Yosei says: Has fulfilled his obligation. Rabbi Yehuda says: Has not fulfilled his obligation. One who recites out of order - has not fulfilled his obligation. One who recites and makes a mistake - should return to the place where he made the mistake. ”

“ If he doesn't know where he erred, he should return to the last place he's sure he recited correctly, such as the beginning of the paragraph. If he doesn't know where he erred at all, he should start over (per Berakhot 16a) . ”