If I recall correctly, Chovos HaLevavos writes (I don't remember where) that there are three types of activity: obligatory, prohibited, and "optional".
On the other hand, Rambam seems to indicate (Hilchos Talmud Torah 3:4) that Talmud Torah is incumbent at all times whenever you are not doing a mitzvah that only can be done by you.
So the question is, if I have to use all my spare time for Talmud Torah, then how can there be a possibility of "optional" activities? Unless the optional activity itself is a mitzvah that only I can do. But is that reasonable?
Yishai Rasowsky, Israel
Shalom R' Yishai,
Your question is a very elementary and essential question. I think answering it is certainly permitted according to all Shitos!
Let me start off from the point you started from. If you go through the Chovos ha'Levavos once again (Avodas Elokim 4), you will be surprised to see that although he begins with what you quoted (that there are three categories: obligatory, prohibited, and optional), he goes on to explain at length that there is not really a third category, since a Jew is supposed to minimize this category only to what he really needs; he should eat just as much as he needs, etc. He concludes that really, there are only two categories, because you need to "use" this category only for what is really needed, and when you do so, those "optional" actions are a Mitzvah too. On the other hand, if one uses that category more than needed, his actions are considered prohibited.
In any case, understanding the Rambam correctly is a challenge, so let's try to make some order in this Sugya of the "Shi'ur" of the obligation to learn Torah.
A) If we look through Hilchos Talmud Torah of the Rambam, we will see pretty clearly that there are different statuses of the obligation of Talmud Torah. In chapter 1:8, the Rambam states that every person is obligated to study Torah in the morning and in the evening. This Psak comes from the Gemara (Nedarim 8a, Menachos 99b), and is also the Psak in the Shulchan Aruch (YD 246).
In chapter 3 it seems that there is a basic way of fulfilling this Mitzvah, and there is a higher way if a person wants to obtain the "crown of Torah."
Then there is the famous Rambam at the end of Hilchos Shemitah v'Yovel that the sons of Levi committed themselves to learning Torah their whole life, but anyone who has this longing to be like Bnei Levi is invited to join them. This shows clearly that the obligation to learn Torah constantly is not a clearcut one according to the Rambam. Besides the obvious reality that not all people are intellectually endowed enough or have the spirit to learn Torah all the time, it is clear also in the text. The basic obligation is setting a fixed time in the morning and in the evening. More than that depends on the person, what his possibilities are, financially and intellectually.
B) The Ran in Menachos seems to say that a person is obligated to study Torah every single moment as he holds there are different opinions in the Gemara, and the Halachah follows the Rabanan's view. The Vilna Ga'on (Shenos Eliyahu, Pe'ah 1:1) seems to agree with the Ran, that if one does not learn every moment that he can, he is not fulfilling the obligation of Talmud Torah.
C) On the other hand, there is an interesting Radbaz (3:859) who disagrees with the above and says that besides citing the Shema in Shacharis and Arvis, there is no more obligation to study Torah. It is of course a higher degree, but not obligatory. He says that this is the opinion of many Rishonim -- Rashi, Tosfos, Rash, Ritva, and Rashba.
D) Many Acharonim follow what seems to be the Rambam's position, as I wrote above, including the Rema (YD 246), Bi'ur Halachah (OC 156), Or Same'ach (Hilchos Talmud Torah 1;4), Birkas Shmuel (Kidushin 27:4), Nefesh ha'Chayim (1:8), and many more.
I tried to give a brief summary, but I must say that this topic has been discussed at length in hundreds (maybe thousands) of Sefarim throughout the generations. This just proves what an important question this is to all.
Kol Tuv,
Aharon Steiner