Now faith is the assurance of things hoped for, the conviction of things not seen. (Heb 11:1)I'm not sure I agree. I don't think this is a definition as much as a description of its effect.
First, consider the sentence. What does it mean? Here the author of Hebrews says of faith that it is the conviction of the unseen, the assurance of things hoped for. That is, faith in this passage is standing squarely in the air. There is nothing underneath it. There is nothing seen, nothing sure. You're looking at something that others can't see (and, technically, you can't either) and saying, "There it is because I have faith." That borders on lunacy. You seem to be saying "I am hoping for something based on simply believing." That looks very unwise. Worse, is this agreeing that faith and evidence are contradictory? Is this defining faith as belief in things that have no basis?
I don't think we have to go there. First, the definition of the word used here, according to Strong's, is "to be convinced (by argument)", "to assent (to evidence or authority)". I didn't put those parentheticals in there; that was according to Strong's. The word means to have a conviction or to be persuaded, but it doesn't require "in a vacuum". It implies "for a reason or reasons". Maybe it's argument; maybe it's evidence. But it isn't mere credulity; it is to be convinced.
Let me give a biblical example. When the Israelites were in captivity in Egypt, they cried out to God for help (Exo 2:23). God, in His mercy, sent them help in the form of Moses. Their response? "May the LORD look upon you and judge you, for you have made us odious in Pharaoh's sight and in the sight of his servants, to put a sword in their hand to kill us." (Exo 5:21) Yes, there it is, a glorious burst of faith on the part of Israel in the helper God has sent them. Not! No, they were worse off than before. But time went by. They watched a total of 10 plagues -- 10 judgments from God -- fall on Egypt and not on Israel. This required no faith. It just happened. In the end, this group that cursed Moses were happy to grab their belongings (and a lot of the Egyptian belongings around them) and head out of Egypt. And in their exit, when Pharaoh once again changed his mind and pursued them, they found themselves between an army and a sea. So what would possess this odd band of people, when they saw a sea split in two and dry ground to cross, to walk into such a treacherous place? Why would they think they could do it safely? That, dear reader, is faith. This faith was built on experience. They saw God work over and over and over again (sight). Now, with waters parted, with something hoped for (freedom and safety) and something unseen (whether or not they would come through the sea alive), they walked forward ... on faith.
Faith is the thing that gives substance to things we can't see and certainty to things we only hope for. But faith does not operate in a vacuum. It is based on evidence, the evidence that God has supplied in His Word and in His character and in His past actions. It enables us to go from the known to the unknown with confidence not because we're blind believers, but because we've seen what God can do and have good reasons to think He can do it again. That is the faith that produces confidence in that which isn't readily apparent. That is the faith that enabled the people described in the faith chapter to do what they did. That is the faith on which you can walk through the toughest times with confidence.