C. F. Keil and Franz Delitzsch on Proverbs 15:2

Pro 15:2

The πραΰ́της σοφίας (Jam 3:13) commended in Pro 15:1 is here continued:

The tongue of the wise showeth great knowledge,

And the mouth of fools poureth forth folly.

As היטיב נגּן, Isa 23:16, means to strike the harp well, and היטיב לכת, Isa 30:29, to go along merrily, so היטיב דּעת, to know in a masterly manner, and here, where the subject is the tongue, which has only an instrumental reference to knowledge: to bring to light great knowledge (cf. 7a). In 2b the lxx translate στόμα δὲ ἀφρόνων ἀναγγέλλει κακά. From this Hitzig concludes that they read רעות as 28b, and prefers this phrase; but they also translated in Pro 13:16; Pro 14:28; Pro 26:11, אוּלת by κακίαν, for they interpreted the unintelligible word by combination with עולת, and in Pro 12:23 by ἀραῖς, for they thought they had before them אלות (from אלה).