I double posted so you would know I've made my argument.
Sorry for the delay, but I'll kick things off now, here's my determinist argument (remember this isn't necessarily what I believe, I said I was happy to take either side-
The reason why we have no free will is because what is claimed by the libertarians (I think that's the word, anyway they're the people who argue that we have free will) to think freely is actually a contingent entity.
Aristotle distinguished between the possible(or passive, can't remember, but I'll just call it possible) intellect, and the agent intellect. Basically, the possible intellect contains all knowledge that individual human has. It containts every thought/idea that that person could conceive. The agent intellect, on the other hand, is specifically what a person is thinking at a given time.
So at time t, a person may be thinking X. So at time t, the agent intellect contains the thought X.
Unless I've misinterpretted Aristotle (which even if I have, it doesn't really affect my argument), the agent intellect is what we consciously think.
Now our conscious mind appears to be free, we appear to be free thinkers. However, before we can get thoughts into our conscious mind, or agnet intellect, they have to come from the possible intellect, which is the storage room for everything we know, so to speak.
The free will debate is essentially about whether we freely chose to think thought X, or whether if we were determined to. I'm going to show now why it is determined.
If thought X is what we're currently thinking, how can we have freely chose what we are currently thinking? If X is our current thoughts, and we freely chose X, what we use to freely chose x would be... you guessed it, other freely chosen thoughts. So essentially,the libertarians are arguing that we're using thought X to chose thought X, which is circular.
The issue is, at time t, we are thinking of X. However, thought X is not all knowledge stored in our mind. Here's how we arrive at a thought.
Y(all possible knowledge) -> thought X. The question is whether the arrow part of the picture was done by free choice or not. But if thought X is the only thing we can consciously analyse, how can we say the movement from Y to X is freely done, when we can only experience X? It's like saying you could see the world before you were given vision.
So ultimately, we do not have free choice, because what we experience in our minds (X), comes from Y, yet we do not experience Y, or the movement from Y to X. If we truly had free will, we could experience Y as well as X, but we can't.
To have free will, not only would we need to experience X, but we would need to able to consciously experience Y (which remember, is all knowledge stored in the particular individuals' brain, Y is pretty much all the Xs a person has). We would begin iwth experiencing Y, then chose which Xs(thoughts we like), but we don't do that, that process is already done for us, hence why all we can experience is X.