Our Gemara relates that Rabbi Hanina ben Agil asked Rabbi Ḥiyya bar Abba about one of the differences between the Ten Commandments as they appear in Sefer Shemot (Chapter 20) and as they appear in Sefer Devarim (Chapter 5). Specifically, his question was why in Sefer Shemot the word tov – good – does not appear, and in Sefer Devarim it does: in connection with the commandment to honor one’s parents the Torah gives a reason: “Le-ma’an yitav lakh – so that it will be good for you.” (15:5)
Rabbi Ḥiyya bar Abba responded that he could not comment on the reason for the appearance of the word tov, since he was not certain that the word appeared in the commandments in Devarim, and recommended that he ask Rabbi Tanhum bar Hanilai who was Rabbi Yehoshua ben Levi’s student, who was expert in aggada. Rabbi Tanhum bar Hanilai responded that since the first set of Tablets were ultimately going to be destroyed, the word tov was not included.
Although every Jewish child studied the Torah and many knew it by heart, not all of the Sages continued to focus on text study. Rabbi Hiyya bar Abba was known as an individual whose focus was on Jewish law, as opposed to his colleague, Rabbi Abbahu, whose area of expertise was aggada.
Many of the commentaries offer alternative explanations for the ignorance apparently shown by Rabbi Ḥiyya bar Abba. The Ria”f suggests that Rabbi Ḥiyya bar Abba’s statement that he did not know whether the word tov was written in the Ten Commandments actually referred to the question about which version contained the actual words that were handed down from God to Moses. Since he felt that we do not truly know what was in the version of the commandments that was broken, he could not respond to the question.