We know with much greater clarity that our will is free than that everything that happens must have a cause. Could we therefore not reverse the argument for once, and say: our conception of cause and effect must be very erroneous because our will could not be free if our idea of cause and effect were correct?
This is essentially right and invites commentary. Which of the following propositions is better known, more evident, more credible, or more likely to be true?
1. With respect to some actions and omissions, the human will is libertarianly free, free in the 'could have done otherwise' sense.
2. Every event, including every action and failure to act of a human person, is the terminus of a causal chain extending into the past to times prior to the person's birth, and every event is as such necessary given what has gone before.
Given that the propositions cannot both be true, if (1), then ~(2). One can now argue either my modus ponens to (~2) or by modus tollens to (~1). Lichtenberg is suggesting in effect that the modus ponens argument is to be preferred.
I agree. For I know directly, in my own case, that I am morally responsible for some of my actions and failures to act, and that therefore I am free with respect to these actions and omissions. This is surely better known than that every event is necessitated by earlier events, and that nothing I do or leave undone is ever something for which I am morally responsible. The direct, first-person evidence trumps third-person considerations. If you balk at my use of 'know,' then I will say that it is more evident, clearer, more likely to be true, more credible, that I am free.
Think about it. How do you know that every event has a cause that necessitates it? It is not a conceptual or analytic truth like Every effect has a cause. That's true ex vi terminorum. But there is nothing in the concept event or the meaning of 'event' that warrants the inference that every event has a cause. Uncaused events are thinkable without contradiction.* Nor do you know the relevant principle by experience. Have you examined every event? No. But even if you had examined every cause-effect sequence in the universe, you could not find the necessity by experience. As Lichtenberg's man Kant famously said, "Experience teaches what is the case, but not what must be the case." For Kant, the causal principle is synthetic a priori. But now: how clear is the very concept of the synthetic a priori, first, and second, how clear is it that the causal principle is an instance of it? And third, how clear are the pillars of the Kantian edifice that undergird the synthetic a priori?
One might reach for inference to the best explanation. What is the best explanation of the success of the natural sciences in the explanation, prediction, and control of natural phenomena? That (macro)nature is deterministic. But the inference is shaky and less to be relied upon than the direct evidence that here and now I did something I (morally) should not have done, something I know I could have refrained from doing.
It is not absolutely self-evident that I am morally responsible and libertarianly free, but it is evident, and indeed more evident than the premises of any deterministic argument. That's enough.
One should never philosophize in such a way that one denies or discounts the very phenomenological evidence that got us philosophizing in the first place.
And if I have good reason to believe that something is the case, then I have good reason whether or not I can solve every puzzle to which the thing gives rise.
You say free will is an illusion? I say that that is nonsense and that you are playing fast and loose with 'illusion.'
*Of course I am not saying that my free actions are uncaused: an uncaused event is not eo ipso a free event. My free actions are caused by me, the agent. I am their creative source, their agent-cause. The idea is not entirely clear, granted. But it is even less clear that I am a deterministic system.