- Is tzitzis a חובת גברא or a חובת טלית?
Tannaim disagree if טלית כפולה – a garment which is worn folded requires tzitzis at the corners of the crease. Rava bar Rav Nachman did, and the garment unfolded, leaving the tzitzis in the middle of the garment. When Rabbah bar Huna commented that these tzitzis do not fulfill the "כנף" mentioned in the Torah, Rava bar Rav Nachman took it off and put on another garment. Rabbah bar Huna said: מי סברת חובת גברא הוא – Do you think that [tzitzis] is a personal obligation, and only applies to a garment which is worn? חובת טלית הוא – It is an obligation relating to the garment, requiring every four-cornered garment which one owns to have tzitzis, even when not being worn. Therefore, זיל רמי לה – go place [tzitzis] on [the garment you removed]. Later, Shmuel says: כלי קופסא חייבין בציצית – articles of clothing left in a drawer are obligated in tzitzis, because he holds tzitzis is a חובת טלית. However, he agrees that a garment made for a burial shroud does not require tzitzis, because the passuk says "אשר תכסה בה" – with which you cover yourself, and האי לאו לאיכסויי עבידא – this one is not made for covering a living person.
- Doing טצדקי to avoid the mitzvah of tzitzis, punished during a time of ריתחא
The Gemara stated that a מלאך disagreed with Rabba bar Huna (that tzitzis is a חובת טלית): a מלאך once found Rav Ketina wearing a linen cloak, which the Rabbis had exempted from techeiles. The מלאך said to him, “Ketina, Ketina, סדינא בקייטא וסרבלא בסיתוא – since you wear a linen cloak in the winter, and a woolen cloak with rounded corners in the summer, ציצית של תכלת מה תהא עליה – what will become of the mitzvah to have tzitzis with techeiles?” Rav Ketina responded: ענשיתו אעשה – “Do you punish for not fulfilling a positive commandment in which one is not obligated?" The מלאך replied: בזמן דאיכא ריתחא ענשינן – “At a time when there is Heavenly anger, we do punish even those who do not fulfill mitzvos such as tzitzis.” The Gemara assumes this punishment would not apply if tzitzis was a חובת טלית, since his garments are not obligated in tzitzis. However, it counters that even if tzitzis is a חובת גברא, it certainly only applies when one wears a garment obligated in tzitzis!? Therefore, it concludes that the מלאך was telling him: טצדקי למיפטר נפשך מציצית – you appear to be employing tactics to exempt yourself from tzitzis, and that is the cause for punishment.
- The required number of threads, placement on the garment, and minimum length
A Baraisa asks: כמה חוטין הוא נותן – how many threads does one place for tzitzis? Beis Shammai requires four, but Beis Hillel requires only three. וכמה תהא משולשת – And how much should it hang down? Beis Shammai says four fingerbreadths, and Beis Hillel says three, but is referring to larger fingerbreadths which are four per tefach, not five. Rav Pappa clarifies that a Biblical tefach equals ארבע בגודל – four fingerbreadths measured with the thumb, which is six with the little finger, and five with the middle finger. Rav Huna rules that tzitzis is made of four threads, attached within four אצבעות of the garment’s edge, and should hang down four אצבעות. Rav Yehudah says it is made of three threads, attached within three אצבעות of the garment’s edge, and should hang down three אבצעות. Rav Pappa concludes with the halachah: ד' בתוך שלש משולשת ארבע – it is four threads, attached within three אצבעות of the garment’s edge, and hangs down four אצבעות. The Gemara objects that a Baraisa teaches that the elders of Beis Shammai and Beis Hillel ruled that tzitzis have no shiur!? The Gemara answers that they have no maximum shiur, but do have a minimum shiur.