The question ‘do we have free will’ is one that has throughout history been exclusively considered by philosophers and theologians. Only those interested in speculation of the most abstract sort would spend any of their time constructing arguments against something that is so intuitively obvious as free will.
And the intuitive feel that we do have free will is sufficient to convince most people of it’s existence. But given all the knowledge science has bestowed upon us in recent centuries, from psychology to physics, the idea of free will is one that is slowly perishing.
Our understanding of reality essentially grounds out at a) the atomic theory of matter and b) the evolutionary theory of biology. Both of these axioms suggest determinism. Objects can’t choose how fast they fall, and genes can’t choose if they survive the darwinian process.
The only other force of nature seems to be randomness. In evolutionary terms, gene mutations can be completely random. But determinism + randomness doesn’t get you free will; it just means that sometimes the causal process throws dice.
What we do know is that decision making (and consciousness and general) is largely reducible to brain processes. Damaging the prefrontal cortex results in increased sexual and aggressive behaviours; the capacity for emotional response is crippled when the orbitofrontal cortex suffers a blow; the examples of brain processes correlating with behaviour can go on seemingly endlessly.
And even more convincingly, our decision making is always beholden to whatever stimuli we are presented with. ‘Unconscious triggering’ documents the phenomena of being able to consistently predict people’s behaviour when providing them with correct stimuli: exposure to aggressive words makes people more confrontational; resumes are assessed more leniently when the asserer is holding a warm hug; pictures or words associated with the elderly make people walk slower.
What’s common across all these scenario’s is that you have have far less control over yourself than it might seem. You aren’t the architect of neuronal firing in your brain, and you don’t control how your brain reacts to external stimuli.
If you are religious, or for whatever reason believe in the existence of a ‘soul’, then this problem becomes much easier for you, as there is now some undiscoverable, intangible entity which can interrupt and manipulate the causal process of synaptic exchange.
But for the rest of us, we have to grapple with what we can empirically discover, and time and time again psychology and neuroscience have revealed that we are slaves to our brain, and puppets of our environments. Simply put, in a deterministic world there is no room for free will.