Matthew Poole and continuators on James 3:12

12 Can the fig-tree, my brethren, bear olive berries, either a vine figs ? So can no fountain yield both salt water, and fresh .

The same Tree cannot ordinarily bring forth Fruit of different kinds (on the same Branch, whatever it may on different, by engrafting) much less contrary Natures. See Mat. 7.16, 17, 18.

Or, neither can a salt Fountain yield fresh Water; but the Scope is still the same, as in our reading. The Apostle argues from what is impossible, or monstrous in Naturals, to what is absurd in Manners, q. d. it is as absurd in Religion, for the Tongue of a regenerate Man, which is used to bless God, to take a liberty at other times to curse Man, as it would be strange in Nature for the same Tree, on the same Branch, to bear Fruits of different kinds; or the same Fountain at the same place to send forth bitter Water and sweet.