Adam Clarke on Proverbs 18:4

The words of a man's mouth - That is, the wise sayings of a wise man are like deep waters; howsoever much you pump or draw off, you do not appear to lessen them.

The well-spring of wisdom - Where there is a sound understanding, and a deep, well-informed mind, its wisdom and its counsels are an incessant stream, מקור חכמה mekor chochmah, "the vein of wisdom," ever throwing out its healthy streams: but מקור חיים mekor chaiyim, "the vein of Lives," is the reading of eight of Kennicott's and De Rossi's MSS., and is countenanced by the Septuagint, πηγη ζωης, "the fountain of life." And so the Arabic. This is the more likely to be the true reading, because the figure of the heart propelling the blood through the great aorta, to send it to all parts of the animal system, is a favourite with Solomon, as it was with his father, David. See the note on Psa 36:9; Pro 10:11, etc.