Adam Clarke on James 3:11

Doth a fountain send forth - sweet water and bitter? - In many things nature is a sure guide to man; but no such inconsistency is found in the natural world as this blessing and cursing in man. No fountain, at the same opening, sends forth sweet water and bitter; no fig tree can bear olive berries; no vine can bear figs; nor can the sea produce salt water and fresh from the same place. These are all contradictions, and indeed impossibilities, in nature. And it is depraved man alone that can act the monstrous part already referred to.