And Moses sware on that day (cf. Numbers 14:21-24; Deuteronomy 1:35, Deuteronomy 1:36). Keil raises the difficulty that in the above passage not Moses, but God is said to have sworn, and that no special inheritance is promised to Caleb, but only that he shall enter the promised land.
But this is not the fact, as a comparison of this passage with Deuteronomy 1:36 will show. That either passage gives the ipsissima verba of Moses is unlikely. The main sense of the promise is given in each.
And there is no impropriety in speaking of the proclamation by Moses of God's decree as an oath pronounced by Moses himself.