New Revised Standard Version
I turned my mind to know and to search out and to seek wisdom and the sum of things, and to know that wickedness is folly and that foolishness is madness.

Contemporary English Version
So I decided to learn everything I could and become wise enough to discover what life is all about. At the same time, I wanted to understand why it's stupid and senseless to be an evil fool.

New American Bible
I turned my heart toward knowledge; I sought and pursued wisdom and its design, and I recognized that wickedness is foolishness and folly is madness.

Douay-Rheims Bible
I have surveyed all things with my mind, to know, and consider, and seek out wisdom and reason: and to know the wickedness of the fool, and the error of the imprudent:

I have surveyed all things with my mind, to know, and consider, and seek out wisdom and reason: and to know the wickedness of the fool, and the error of the imprudent:

I applied mine heart

Ecclesiastes 1:13-17 And I proposed in my mind to seek and search out wisely concerning all things that are done under the sun. This painful occupation hath God given to the children of men, to be exercised therein. . . .

Ecclesiastes 2:1-3,12,20 I said in my heart: I will go, and abound with delights, and enjoy good things. And I saw that this also was vanity. . . .

the reason

Ecclesiastes 7:27 Lo this have I found, said Ecclesiastes, weighing one thing after another, that I might find out the account,

Ecclesiastes 2:15 And I said in my heart: If the death of the fool and mine shall be one, what doth it avail me, that I have applied myself more to the study of wisdom? And speaking with my own mind, I perceived that this also was vanity.

Ecclesiastes 3:16,17 I saw under the sun in the place of judgment wickedness, and in the place of justice iniquity. . . .

Ecclesiastes 9:1,2 All these things have I considered in my heart, that I might carefully understand them: there are just men and wise men, and their works are in the hand of God: and yet man knoweth not whether he be worthy of love, or hatred: . . .

Jeremiah 12:1,2 Thou indeed, O Lord, art just, if I plead with thee, but yet I will speak what is just to thee: Why doth the way of the wicked prosper: why is it well with all them that transgress, and do wickedly? . . .

2 Peter 2:3-9 And through covetousness shall they with feigned words make merchandise of you. Whose judgment now of a long time lingereth not: and their perdition slumbereth not. . . .

2 Peter 3:3-9 Knowing this first: That in the last days there shall come deceitful scoffers, walking after their own lusts, . . .

know

Ecclesiastes 9:3 This is a very great evil among all things that are done under the sun, that the same things happen to all men: whereby also the hearts of the children of men are filled with evil, and with contempt while they live, and afterwards they shall be brought down to hell.

Ecclesiastes 10:13 The beginning of his words is folly, and the end of his talk is a mischievous error.

Genesis 34:7 Behold his sons came from the field: and hearing what had passed, they were exceeding angry, because he had done a foul thing in Israel, and committed an unlawful act, in ravishing Jacob's daughter.

Joshua 7:13 Arise, sanctify the people, and say to them: Be ye sanctified against tomorrow: for thus saith the Lord God of Israel: The curse is in the midst of thee, O Israel: thou canst not stand before thy enemies, till he be destroyed out of thee, that is defiled with this wickedness.

2 Samuel 13:12 She answered him: Do not so, my brother, do not force me: for no such thing must be done in Israel. Do not thou this folly.

Proverbs 17:12 It is better to meet a bear robbed of her whelps, than a fool trusting in his own folly.

Proverbs 26:11 As a dog that returneth to his vomit, so is the fool that repeateth his folly.