The other day when work ended, rather than go to my car and drive home as I have every day for the last four years, I just sat outside the building for no reason at all. Maybe I didn't want to go home just yet; maybe I was tired; maybe this maybe that. I sat for about 30 minutes, almost without moving, before finally leaving. I was thinking and thinking about why I did it, and then I started to wonder why I felt anxious about not being able to answer the question. Is it possible we've all been brainwashed into accepting the - if I remember this correctly - "principle of sufficient reason" (assuming this states that all things happen for a reason). Is it possible I sat down for no reason at all?

This principle of sufficient reason (PSR) in its modern form is usually associated with Leibniz, though its origins seem to go much further back. It claims that for anything that exists or for any event, there exists some reason that explains its existence or occurrence. While it has implications for human actions like your own, the PSR is not primarily a psychological theory.

It seems to me that for the sake of fulfilling PSR, all we have to say is that the cause of your 'sitting and staring for 30 minutes' is that it happened because you chose to do so. There's probably much more we could say about your actions: maybe you did so because you needed rest, or maybe you had a sub-conscious motive that you were not completely aware of.

Like all universal laws/principles, PSR is very difficult to establish with certainty. Even if everything I've observed appears to have a sufficient reason, I can't be certain that I'm correct in attributing those things and events to the reasons I associate with them. It also doesn't mean that the next event will definitely have a sufficient reason. But, that being said, if we don't presuppose PSR, knowledge can't advance far at all. Furthermore, it certainly seems that everything we observe does have a sufficient reason. So, I tend to think that PSR is very likely to be true and has as much justification as any other 'law of science.'

Professor Silverman is right about the PSR and how it relates to your question (though I'm not sure I agree that "it certainly seems that everything we observe does have a sufficient reason"). But perhaps you were also wondering if your action (or inaction) happened for no reason in this sense: it was caused by factors that you were unaware of and you would not think of as reasons at all (much less good reasons). Maybe it was caused by some random thing a co-worker said to you or by some unnoticed aroma or by some neural glitch. In these cases, it might be right to say you sat down "for no reason at all" (even if something causally explains the event).

Another possibility is that nothing causally explains the event. Quantum mechanics gives us a model for probabilistic causation, such that given exact conditions X (e.g., electron being shot at barrier), there is some objective chance A will follow (e.g., electron being deflected) and some objective chance B will follow (e.g., electron penetrating barrier) and nothing explains why A rather than B happens or vice versa. It is not implausible that something like this can occasionally happen in large-scale events, such as human actions, perhaps because quantum indeterminism occasionally influences large-scale events.

For instance, it just might have been that your exact condition X involved a very complex neural state that had some objective chance of leading to A (your getting in car) and some objective chance of leading to B (your sitting down) and nothing explains why B happened rather than A.

While some people (e.g., Robert Kane) have used this sort of model to ground a theory of free will, I think such indeterminism would not help secure free will (it gives us no more control or responsibility over our lives than without it), though it might put some pressure on the principle of sufficient reason.

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