How do we know that we have free will? Surely if everything was pre-determined for us, we wouldn't know. Why are people so sure that free will actually exists?

There's a theory that there are an infinite number of parallel universes out there. Basically every time we come to a decision point and turn right instead of left, the universe splits and and there's a version where you turned left. So if in infinite realities we've done it all, then we have the free will to make our own choices.... And every destiny will come to pass somewhere.

I've also heard a similar theory about God and creation. At the moment of creation he saw every possible path. So we have free will, but no matter what we choose, God knows where it leads. Free will and predestination wrapped up in God's mind.

There is no way to KNOW for certain, either way.

However, in most sects of the Christian religion, free will is assumed.  Why?  Because without free will, then one has no control over whether one goes to Heaven or Hell in the afterlife.  Without the choice of free will - that means that God predestined people's afterlife.  Which would make God the opposite of the "kind, caring, parent figure" they want Him to be.

Basically ... "free will" lets God off the hook for all the bad things that happen.  Whereas "predetermination" lets people off the hook for their actions.

"Free Will" is an invented term by man to feel empowered to be the ambassador of his own destiny. Most Christian religions push "Free Will" as "Their" part in receiving grace and choosing God.

This is NOT the case, "Free Will", in it's inception, was the understanding WE HAD of conscious decisions we THINK we make. We know now that many decisions we make are based solely on impulsive choices the brain makes, that we gain consciousness later on. We are products of:

1.) Genetics

2.) Environmental Influences

3. Experiences we've had, both good and bad in our lives.

Here is an excellent discussion on "Free Will" as it really is -

youtu.be/_FanhvXO9Pk

A key part of our mental and emotional makeup is free will. Yes, God implanted in us the faculty of freedom of choice. It was indeed a wonderful gift from him.  So the desire for freedom is no accident, for God is a God of freedom. The Bible says: “Where the spirit of Jehovah is, there is freedom.” (2 Corinthians 3:17) Hence, God gave us free will as part of our very makeup. Since he knew the way our minds and emotions would work, he knew that we would be happiest with free will.  To go with the gift of free will, God gave us the ability to think, weigh matters, make decisions, and know right from wrong. (Hebrews 5:14) Thus, free will was to be based on intelligent choice. We were not made like mindless robots having no will of their own. Nor were we created to act out of instinct as were the animals. Instead, our marvelous brain was designed to work in harmony with our freedom of choice.