I have already addressed the more extreme and bizarre versions of associating determinism with fatalism, the versions where determinism is some kind of external force that you can trick or fight against. But there are more subtle versions of this confusion as well, which are not as clearly wrong or bizarre, and therefore are worth addressing.
I want to address two specific sort of arguments here. The first is that determinism is incompatible with knowledge, and is similar to an argument used by Christian apologists about the incompatibility of evolution with knowledge. The apologist argument is that we should not expect evolution to have brought about a brain which generates truths, and that the human brain would be fundamentally unreliable if evolution was true. There are many things we can reply to this, but the main objection is that the brain is not a proposition-generating machine but rather a versatile tool which, like other parts of our body, can be used for many different purposes. One of these purposes happens to be finding rationally justified propositions.
The anti-determinist argument is somewhat similar to this, but basically replaces evolution with determinism. If determinism is true, then our thoughts are the result of predetermined processes in the brain, therefore we cannot assume that our beliefs are correctly justified. This is usually accompanied by a fallacious argument from incredulity: how can we assume that any proposition that is the result of random natural processes will be properly justified?
The main fallacy with this argument is the assumption that natural processes are random or unguided. Everything humans do is determined and regulated by natural law, and yet we don’t say that buildings or computer chips are random, came into existence unguided, or necessarily unreliable. If it would be laughable to assume this in the case of buildings or computer chips, then why should we assume it in the case of human reasoning? When I construct an argument and justify it rationally, am I not acting in a determined manner and in accordance with natural law? The main difference is that a building is an entirely physical product while an argument is a conceptual product, but both require the careful use of our minds in constructing justified beliefs (about construction or about concepts).
Saying that a thought was determined instead of volitional does not change the nature of the thought, or its justification or absence thereof. The only way we can tell whether a proposition is justified remains to look at arguments or lines of reasoning in favor of, or against, it. What I believe about, say, the sky being blue still hangs upon observations of the sky and the facts about light passing through air, regardless of how my brain arrived at the proposition. For that matter, a Markov chain algorithm could theoretically compose an entire argument (with premises, logic, and conclusion) on some subject: the argument would still be true or false on its merits, regardless of the fact that it was the result of an unthinking algorithm (note that I am not arguing that we are anything like a Markov chain algorithm!).
This argument also begs the question of how a volitional brain could use evidence to formulate reasoning. After all, we are told that volition is not affected by physical processes, since anything caused by a physical process is determined. Perceiving evidence is a physical process. So how can a volitional brain process evidence?
The second argument I wanted to discuss is one which attacks the ethical consequences of determinism. In its simplest version, the argument is simply that determinism cannot explain why people change their minds, or how people can consider arguments and “choose” one side over the other. Sometimes this takes the ironic form that determinists are self-contradictory because they are trying to change people’s minds about agency, when that is impossible according to determinism.
This argument always puzzles me because there is no logical connection between determinism and being unable to be convinced by an argument. All that determinism says is that the processes in our brain are the result of natural processes. It does not indicate anything about the kind of thoughts we can or cannot have. Of course we can change our minds, as is demonstrated every day. Indeed, most or all determinists arrived at their position because some argument or discussion changed their minds on the subject. It would be very silly for a determinist to deny that we can change our minds, but we don’t need to, since there is no logical argument going from “determinism is true” to “we cannot change our minds.”
Sometimes the argument is actually backed by a kind of fatalism: people cannot help being what they are. But this is not a position about whether natural law applies to the brain, this is a psychological position. Whether human beings have some “true nature” which is always reflected in their thoughts or actions or not, this has nothing to do with determinism. You can believe in “fixed personalities” (to give a name to this belief) and be a determinist or an anti-determinist, and you can believe that there are no “fixed personalities” and be a determinist or an anti-determinist.
I think the idea that there are “fixed personalities” is silly because people do change their minds. Nothing about this fact has anything to do with determinism, except the obvious conclusion that such changes take place within the realm of natural law, i.e. are a psychological result of some prior psychological cause. Some people are more set in their ways and less likely to change, while others are more tolerant of new attitudes or ideas. This is a very interesting subject, but, again, it has nothing to do with determinism.