'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?

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.

In the morning put your seed into the earth, and till the evening let not your hand be at rest; because you are not certain which will do well, this or that--or if the two will be equally good.

Have joy, O young man, while you are young; and let your heart be glad in the days of your strength, and go in the ways of your heart, and in the desire of your eyes; but be certain that for all these things God will be your judge.