I don't think you have to reject causality if there is free will. why couldn't free will itself be a cause? ...
It {free will} could be the cause {exist}, if one postulates free will comes form an immaterial source or agent - such as a "soul," but if your nerves control your thoughts (or ANY material agent, such as radio or sound waves focused on your skull, etc.) then note these material agents are ALL acting in accord with the natural laws (unless you postulate that on occasions matter is not governed by the natural laws. -I.e. POSTULATE MIRACLES.)
IMHO neither of these postulates has any supporting evidence, but that is not proof that they can not exist.
Just be logically honest. - I.e. admit that either miracles must occur for free will to exist OR some non-material agent gives you free will. One or the other* is needed to escape from the control of the nature laws.
Perhaps the following will help you to see this is the case:
Humans are very complex organisms with introspection as to their reasons for their actions. - Often even when some reason is "understood," it is not fully correct or complete. Humans universally explain some of their actions a "free choices" between alternatives, but studies with electrodes contacting the brain show that in the simple case examined, the subject's brain makes the choice well before (up to a second) before the subject is consciously aware of making any choice.
For example, which of two buttons to push is already reflected in the electrical activity in the "pre-motor cortex," before the conscious choice is made. Clearly consciousness is only INFORMED about the choice, not making it.
This was first demonstrated ABOUT 30 YEARS AGO by Dr. Libbet (Lippet ? not sure now, but last year much better data showing 1 second earlier decision data was obtained by MRI experiments - even the pre-motor cortex is not the first to know! Decision appears to be made in frontal cortex). People under going brain surgery are usually fully conscious with local anasesia only of scalp. The surgeon is constantly talking with them to be sure they do not sue him later if he cuts out parts of brain that leave a serious cognitive or speech defect, etc. -
In the old days prior to cutting, the part of brain** to be cut out was cooled, but now I think quick decay anasesia is used prior to resection.) To tell exactly when the subject THINKS he made the conscious decision, the subject watches a clock with a fast sweep second hand. Soon after the "conscious decision" the subject reports where the clock's sweep second hand was when he consciously decided to push button "A" instead of bottom "B." The decision was already made and quite evident in the electrical active earlier. I.e. the doctor or his assistant knows which button will be chosen before the subject does.
SUMMARY:
This irrefutable evidence shows that your brain makes choices and then informs your consciousness about the choice already made and then you THINK you chose.
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*There may be one possible other escape from the control of natural laws over your every thought and action: For it see:
http://www.sciforums.com/showpost.php?p=1294496&postcount=52
for details, and evidence supporting this non-standard POV. It is a long read, about 8 pages if printed.
But the price is high: You are only non-material information in a simulation.
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**Parts of brain are often removed for intractable focal epilepsy - still the only treatment today. In extreme case, even half of the brain is remove in young children and amazingly theY grow up with no easily (casually) observed defects.