- Machlokes if תכלת and לבן threads are מעכב each other
The fourth Perek begins: התכלת אינה מעכבת את הלבן – the techeiles thread (dyed blue with the secretion of the חלזון) is not essential for the validity of the white thread, and the לבן is not מעכב the תכלת. Thus, if someone has only תכלת threads or only לבן threads, he is יוצא. The תפלה של יד is not מעכב the של ראש, nor vice versa. The Mishnah appears to disagree with Rebbe, who darshens: "וראיתם אותו" - and you shall see it, מלמד שמעכבין זה את זה – this teaches that [the white and the techeiles) are essential to each other, but the Chochomim say they are not מעכב each other. The Gemara explains Rebbe’s derashah: "הכנף" מין כנף – the term “of the corner” implies that tzitzis should be the same type as the “the corner” (i.e., the garment), which was usually white [linen]. The passuk says to add "פתיל תכלת" – a thread of techeiles, and says "וראיתם אותו" – you shall see “it,” implying the tzitzis are not valid עד דאיכא תרוייהו בחד – unless both (לבן and תכלת) are present together. The Rabbonon hold that “it” refers to כל חד לחודיה – each one by itself (i.e., the לבן and the techeiles).
- The mitzvah for the לבן to precede the תכלת is not מעכב
Rav suggested that the Mishnah can agree with Rebbe, because the Mishnah’s statement that לבן and תכלת are not מעכב each other refers to the law of להקדים – one type of thread preceding the other. A Baraisa states: מצוה להקדים לבן לתכלת – it is a mitzvah to put the white threads onto the garment before the techeiles threads, ואם הקדים תכלת ללבן יצא – but if he put on the techeiles before the white he is יוצא, אלא שחיסר מצוה – but he is missing a mitzvah. Rav explains that he completely fulfilled the mitzvah of tzitzis, but missed the mitzvah of the correct order, and לא עבד מצוה מן המובחר – he did not do the mitzvah in the preferred way. The Gemara asks how Rav will explain the Mishnah’s statement that techeiles is not מעכב white threads (since techeiles is not supposed to be first). Rami bar Chama suggests that it refers to טלית שכולה תכלת – a garment made entirely of techeiles, in which case the techeiles should be put on first, but this order is not מעכב. However, Rava objects: מידי ציבעא קא גרים – does the color of the thread determine the order of threads? Since most garments are white, the white threads must always be first, so Rav’s interpretation is rejected.
- גרדומין – Stubs
Rava answers that the Mishnah can agree with Rebbe, and refers to גרדומין – stubs left when threads tear. Thus, the Mishnah is teaching that if the techeiles threads were reduced to stubs and the white threads remain, or vice versa, the tzitzis are still valid. The Gemara asks for the minimum shiur of these stubs, and Shmuel says כדי לענבן – enough to tie them into a slipknot. The Gemara asks if this requires enough to tie all eight threads together into one slipknot, or only to tie each one individually into a slipknot, and this question is left unresolved. Rav Ashi asks, if the threads are אלימי – thick and cannot be tied into a slipknot, but are long enough that if they had been thin, they could have tied into a slipknot, are they valid? Rav Acha brei d’Rava answered: כל שכן דמינכר מצותייהו – certainly, their mitzvah is even more noticeable when the threads are thick, and their thickness cannot detract from their validity.