'Certain' in the Bible

I am certain that there is nothing better for a man than to be glad, and to do good while life is in him.

I am certain that whatever God does will be for ever. No addition may be made to it, nothing may be taken from it; and God has done it so that man may be in fear before him.

Who is certain that the spirit of the sons of men goes up to heaven, or that the spirit of the beasts goes down to the earth?

There was a certain man without a dependent, having neither a son nor a brother, yet there was no end to all his labor. Indeed, his eyes were not satisfied with riches and he never asked, “And for whom am I laboring and depriving myself of pleasure?” This too is vanity and it is a grievous task.

In the day of wealth have joy, but in the day of evil take thought: God has put the one against the other, so that man may not be certain what will be after him.

No one is certain what is to be, and who is able to say to him when it will be?

Though a sinner does evil a hundred times and his life is long, I am certain that it will be well for those who go in fear of God and are in fear before him.

All this I took to heart, and my heart saw it all: that the upright and the wise and their works are in the hand of God; and men may not be certain if it will be love or hate; all is to no purpose before them.

Sow your seed in the morning and do not be idle in the evening, for you do not know whether morning or evening sowing will succeed, or whether both of them alike will be good.

Rejoice, young man, during your childhood, and let your heart be pleasant during the days of young manhood. And follow the impulses of your heart and the desires of your eyes. Yet know that God will bring you to judgment for all these things.