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לנכרי תשיך. וְלֹא לְאָחִיךָ, לָאו הַבָּא מִכְּלַל עֲשֵׂה, עֲשֵׂה, לַעֲבֹר עָלָיו בִּשְׁנֵי לָאוין וַעֲשֵׂה: לנכרי תשיך UNTO AN ALIEN THOU MAYEST LEND UPON INTEREST (according to Rashi: TO AN ALIEN THOU MAYEST PAY INTEREST) — but not to thy brother. Such a prohibition which is not plainly stated but can only be drawn by inference from a positive command is itself regarded only as a positive command — so that one who pays interest to his brother transgresses two negative commands: לא תשיך in v. 20, ולאחיך לא תשיך in v. 21 and a positive command לנכרי תשיך — ולאחיך לא (cf. Sifrei Devarim 263:1; Bava Metzia 70b; also cf. Rashi on Deuteronomy 14:20).