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

People's New Testament

3:12 Can the fig tree... bear olive berries? Neither does a tree bear two opposite kinds of fruits. Nor should the mouth bear blessing and cursing, good and evil.

Jamieson-Fausset-Brown Bible Commentary

12. Transition from the mouth to the heart.

Can the fig tree, &c.-implying that it is an impossibility: as before in Jas 3:10 he had said it "ought not so to be." James does not, as Matthew (Mt 7:16, 17), make the question, "Do men gather figs of thistles?" His argument is, No tree "can" bring forth fruit inconsistent with its nature, as for example, the fig tree, olive berries: so if a man speaks bitterly, and afterwards speaks good words, the latter must be so only seemingly, and in hypocrisy, they cannot be real.

so can no fountain . salt . and fresh-The oldest authorities read, "Neither can a salt (water spring) yield fresh." So the mouth that emits cursing, cannot really emit also blessing.

Matthew Henry's Concise Commentary

3:1-12 We are taught to dread an unruly tongue, as one of the greatest evils. The affairs of mankind are thrown into confusion by the tongues of men. Every age of the world, and every condition of life, private or public, affords examples of this. Hell has more to do in promoting the fire of the tongue than men generally think; and whenever men's tongues are employed in sinful ways, they are set on fire of hell. No man can tame the tongue without Divine grace and assistance. The apostle does not represent it as impossible, but as extremely difficult. Other sins decay with age, this many times gets worse; we grow more froward and fretful, as natural strength decays, and the days come on in which we have no pleasure. When other sins are tamed and subdued by the infirmities of age, the spirit often grows more tart, nature being drawn down to the dregs, and the words used become more passionate. That man's tongue confutes itself, which at one time pretends to adore the perfections of God, and to refer all things to him; and at another time condemns even good men, if they do not use the same words and expressions. True religion will not admit of contradictions: how many sins would be prevented, if men would always be consistent! Pious and edifying language is the genuine produce of a sanctified heart; and none who understand Christianity, expect to hear curses, lies, boastings, and revilings from a true believer's mouth, any more than they look for the fruit of one tree from another. But facts prove that more professors succeed in bridling their senses and appetites, than in duly restraining their tongues. Then, depending on Divine grace, let us take heed to bless and curse not; and let us aim to be consistent in our words and actions.