Although there are hints that doubts about the existence of 'free will' appeared before Descartes, he clearly believed that the entire universe was completely deterministic. In other words, all actions within the universe could be determined beforehand if sufficient information was available.
Although no one argues that the bulk of the universe is deterministic, at least with regard to all non-volitional entities, it isn't clear that all human actions can be so determined. It is still a subject of hot debate whether humans do or do not possess free will. In this brief note, I argue that a purely deterministic universe cannot be logically defended and that the alternative view that free will exists is the only defensible position.
There are inevitable consequences to the notion that all actions are predetermined. The first is that no choices are possible. If you are predestined to take every action you take, you cannot claim any personal responsibility for what you do and cannot assign praise or blame to any others for their actions. In a universe where no choices are possible, no responsibility is possible. The illusion of free will is only that and not a basis for moral judgments.
Contrast our view of other people with our view of a typewriter. A typewriter is a purely deterministic object, assuming it is functioning. When you press an 'A' key, an 'A' will appear on the paper. The typewriter, as with other deterministic mechanisms, does not choose to print the character. Similarly, your utterances and actions are absolutely beyond your control in a completely deterministic universe. But this fact has further implications, which will be seen in the following paragraphs.
If free will does not exist, neither does knowledge. Why? Because you cannot convincingly claim that any statement you make corresponds to a fact. You can only claim that you are helpless to report otherwise. Just as a running tape recorder can utter that 2+2=5 as easily as it can utter that 2+2=4, you are only capable of uttering that which was predetermined with no regard to any consent on your part.
The inevitable conclusion is that you cannot convincingly argue in favor of a completely determined universe, because your arguments would then be entirely the result of compelled responses. They have no necessary connection with any fact or truth. On the other hand, there is no such objection to arguing in favor of free will. If it exists, you can defend it.
There have been many attempts to delve into the issues surrounding the debate on Free Will vs. Determinism. Quantum mechanics has been studied for its implications on the issue. Many psychological experiments have been devised to shed light on the matter. At bottom, however, the arguments may be addressed on purely philosophical grounds with no reliance on the experimental sciences. The implications with respect to the existence of personal responsibility and the existence of knowledge suffice for everyone to take a position. And which position do people take in their observable lives? They exhibit every confidence that free will does exist, that individuals are responsible for their own choices and that knowledge is possible.