Some post-modern and other thinkers will insist, of course, that this distinction is a bogus one. According to them, "reason” is a term used to dignify what is, in reality, merely another purely causal mechanism for influencing belief, alongside brainwashing and indoctrination. Reason is no more sensitive to the “truth” than these other mechanisms (for of course there is really no truth for it to be sensitive to). Reason is, in reality, just another form of power – of thought control. It is essentially as coercive and/or manipulative as any other mechanism.
But this is to overlook the fact that while a rational argument can, in a sense, “force” a conclusion on you, the “force” involved is normative, not causal. Let me explain...
Causal determination determines what will happen. For example, given the causal power of these rails to direct this train, the train will go to Oxford. Normative determination, on the other hand, determines not what will happen, but what ought to. It is an entirely distinct type of determination.
A rational argument shows you what you ought to believe if you want to give your beliefs the best chance of being true. Take this valid deductive argument:
All men smell
John is a man
Therefore, John smells.
To recognise that this argument is valid is just to recognize that if you believe that all men smell, and that John is a man, then you ought to believe that John smells. But of course this argument doesn’t causally compel you to accept that conclusion even if you do accept the premises. You’re entirely free to be irrational.
This isn't to deny that rational arguments have causal power. Of course they do. A good argument can have the power to change history (consider the wonderful arguments of Galileo, or the campaigner against slavery William Wilberforce). But when rational arguments have the causal power to shape people’s thinking, they typically have it as a result of their having normative power. People change their opinions precisely because they recognize the normative force of the argument.
[Notice, by the way, that we can easily demonstrate that a rational argument doesn’t have normative power simply in virtue of its having the causal power to shape people’s thinking (though critics who fail to understand the difference between normative and causal determination or "force" will obviously miss this point). The obvious counter-example is fallacious argument. A fallacious argument lacks any normative power. But notice that, if the fallacy is seductive, it will still have considerable causal power to shape belief.]
So rational arguments have causal powers. But that is not to say that rational argument is in reality just another purely causal mechanism alongside e.g. brainwashing and peer pressure.
I have stressed how rational argument differs from purely causal mechanisms for influencing belief. First, in the previous post, I explained how rational argument is truth-sensitive, while purely causal mechanisms are typically not. Now I have added the point that, rational arguments, while also possessing causal power to shape belief, typically have this power in virtue of their normative power. The kind of “determination” a rational argument "imposes" on us is, in the first instance, normative, not causal.
Indeed, as I also pointed out in the previous post, when you use reason to persuade, you respect the other’s freedom to make (or fail to make) a rational decision. When you apply purely causal mechanisms, you take that freedom from them. Your subject may think they’ve made an entirely free and rational decision, of course, but the truth is that they’re your puppet – you’re pulling their strings. In effect, by ditching reason and relying on purely causal mechanisms – peer pressure, emotional manipulation, repetition, and so on – you are now treating them as just one more bit of the causally-manipulatable natural order – as mere things.
So to sum up, we have seen that, when it comes to shaping belief, rational argument differs from taking the purely causal route in at least three important ways:
(i) it is truth-sensitive (whereas purely causal mechanisms typically are not)
(ii) while rational arguments can be causally powerful, their causal power typically derives from their normative power – which is a distinct, non-causal form of "power".
(iii) Rational argument allows for an important form of freedom - a freedom that the purely causal mechanisms actually strip from us.
Next time a "post-modern" etc. insists that reason is just another form of manipulative power or thought-control, you might try pointing these differences out...