452. Just White or Just Blue

Tzitzis 1:4

Lacking techeiles does not prevent one from performing the mitzvah of the white and lacking the white does not prevent one from performing the mitzvah of the techeiles. Therefore, if a person does not have techeiles, he should make tzitzis just from the white. Similarly, if tzitzis were made of both white and techeiles and then the white strings broke, leaving just the techeiles, it is valid.

Tzitzis 1:5

While lack of one does not prevent performing the other, the white and the techeilis are not two separate mitzvos; they are one mitzvah. Whether one’s tzitzis are white, techeiles, or both, one fulfills a single mitzvah. The earlier Sages derived this from Numbers 15:39, “They shall be tzitzis for you,” meaning that both items are one mitzvah. Tzitzis on all four corners are necessary because all four constitute a single mitzvah.