I am. I exist, and nothing anybody does or says can convince me that I don't exist. Because I can state my existence, then I must be aware of my existence. Being aware of my existence, I can understand how I interact with the world. Knowing how to interact with the world I can learn how the world works. Knowing how the world works, I can judge the consequences of my actions. Being able to judge the consequences of my actions, I have free will. From the moment we achieved sentience, we possessed free will.
If I have free will, then I must be able to know that I actually have free will.
I must be aware of my own existence before I can contemplate the consequences of my actions. If I do not understand the consequences of my actions, how can I really be said to be choosing? If I were told to pick a number between 1 and 1,000 I would have just as much reason to pick one number as another. There is no way to make a real decision which uses your intellect and awareness, and is therefore essentially choiceless. I do, however, understand the consequences of my actions. Not perfectly, no, but well enough. Because of this knowledge I am able to use my intellect to discover new possibilities and my reasoning to choose which path to take.
If we are at any level of the decision making, then we are at all levels of the decision making. I do not supplicate to a higher authority in the confines of my own head. I assess, I understand, I decide. If my decision is biologically and environmentally conditioned, so what? All those paradigms of our existence (i.e. I rather enjoy breathing, hard work brings about satisfaction) are the outcome of the decisions of all my ancestors. I naturally know how to do many things, like breathe. The choices of my forebears shaped me into this person. My environment is similarly the product of the choices of those that came before, as well as those alive now. Centuries of people acting, living, choosing, creating, destroying, has shaped my world. There is much to be learned from the environment I exist in. As I grow I choose which patterns of thought I want ingrained in me, ready for immediate use. It is only rarely that I need to question the pattern. But at all times I have the ability to choose: do I follow instinct? Do I do as the others have done? Or do I see a new way of being?
Everything has a price, but that doesn't prohibit action. That only deters action. Everyone can choose to do something really stupid sometimes. We have before us a plethora of possibility, and yes, our decisions are weighted. And they are considered. Our choice is our own to make. All of my decisions are mine to make, no matter if the decision is the best one, or the worst. I still made the decision.
The idea of free will is predicated on the fact that I exist.