Just look at this thread. You post. I reply. Your posts determine how I reply.

Observe how you reason. You use reasons to reach conclusions. The reasons determine the conclusions you reach.

How about the concept of free will. You are privy to a certain amount of information at any given moment. That information determines the decisions you can make. You cannot make a decision with information that you don't have. Later, you may acquire new information after you made the decision, but that doesn't mean you would have made a different decision at the time you made it. You would make a different decision now, but the moment of decision is past.

but that doesn't mean you would have made a different decision at the time you made it. You would make a different decision now, but the moment of decision is past. — Harry Hindu

Yes, that's determinism.

To make the case for reasoning being indeterministic we have to assume that there is some neural influence that doesn't behave deterministically, some flakiness - some element of eccentricity and unreliability, like a misfiring neuron.

Then you probably have to accept that this flakiness is sourced from some as yet unknown extra-universal source (exists outside of our universe itself), or that maybe our universe itself is not a singular entity as we perceive it but is a collection of universes and that the flakiness is completely independent of the universe of the stimulus that stimulates it. We don't know. It just comes down to whatever sits right with you. There is no proof or even legitimate evidence for either determinism or indeterminism really.