Foster was a strict teacher, a "brash curmudgeon" to his students, warning them "if you make one stupid mistake, you're out!"; he sometimes assigned a translation of a bawdy text to a pious sister, and a text from St. Augustine or Pope St. Leo the Great to an atheist or a Jew. A former student quoted him dismissing theory and warning his students: "I don't care about your garbage literary theory! ... If you don't know what time of day it is, or what your name is, or where you are, don't try Latin because it will smear you on the wall like an oil spot."