A fool also is full of words: a man cannot tell what shall be; and what shall be after him, who can tell him?
Full of words (Ecclesiastes 5:2) - boasting (as the context implies) of what he will do, how he will live in grandeur.
A man cannot tell what shall be - (Ecclesiastes 3:22; Ecclesiastes 6:12; Ecclesiastes 8:7; Ecclesiastes 11:2; Proverbs 27:1.) If man, universally (including the wise man), cannot foresee the future, much less can the fool; his 'many words' are therefore futile.