Complete Explanation is not Contrastive Explanation

One of the biggest objections to the PSR is that in order for it to work, necessitarianism must be true. Indeed, this is at the heart of Peter van Inwagen’s influential 1984 objection to the PSR (http://alexanderpruss.com/papers/LCA.html - this contains Van Inwagen’s argument and Pruss’ brilliant response to it). After all, how can an explanation be complete if the explanation does not entail the explanandum - what the explanation explains? I think this view of complete explanation is mistaken, and I hope to explain why in this post.


Let’s say that there is a double-slit experiment where there is a right and left slit. Let’s suppose that there is an electron that ends up going through the right slit. The explanation for this will consist in a conjunction of things like: the nature of the experiment, the external factors in the experimental environment, the fact that there was at least a 50% chance that the electron went through the right slit before it actually did, etc. The objector will respond: “but this is not a complete explanation; in order to have a complete explanation of why the electron went through the right slit, we must have an explanation of why the electron went through the right slit rather than the left slit.” I think this is mistaken for the simple reason that the electron did not in fact go through the left slit. It seems very plausible to think that the PSR only applies to things that exist: facts or states of affairs. Given this, the reason that the complete explanation of why the electron went through the right slight does not consist in the explanation of why the electron went through the right slit rather than the left slit is because since the electron did not go through the left slit there is literally nothing to explain. There is no truthmaker for the electron going through the left slit because the electron did not in fact go through the left slit so there is no need to explain why it didn’t for there is nothing to explain. I would like to note that my use of the word “truthmaker” is simply for the sake of ease and that what I have explained above is the case of any theory of truth because on any theory of truth, if the electron did not go through the left slit, there is nothing to explain because the electron did not go through the left slit: there is nothing there.


I think this point becomes even clearer when we compare deterministic cases with indeterministic cases. For example, let’s say that a rock falls to the ground and let’s suppose that this is a deterministic case: given gravity, the rock necessarily falls to the ground. In this case, what is the explanation of why the rock falls rather than not falling? Gravity. Now compare this with the indeterministic case of the electron going through the right slit: what is the explanation of why the electron went through the right slit rather than the left slit? The conjunction of the nature of the experiment, the external factors in the experimental environment, the fact that there was at least a 50% chance that the electron went through the right slit before it actually did, etc. 


So, I think that complete explanation is not contrastive explanation and I think this has explained why.

Comments

  1. theunnoticableFebruary 3, 2022 at 5:14 PM

    Wouldn't there be a potential for the electron to go through the left slit, and so there wouldn't be
    literally nothing? It would seem that the potency for going left would need to be explained, then. The question would be: why is it in potency rather than reduced to actuality?

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    Replies
    1. The Engaged ThomistFebruary 4, 2022 at 11:09 PM

      This is a good response. I think this just pushes it back a step and so the explanation of why the potential to go through the right slit is actualized would just be things like the experimental set-up and so on. Now, if we ask what is the explanation of why the potential to go through the right slit was actualized rather than the potential to go through the left slit, will just be the explanation of why the electron went through the right slit as there is no truthmaker for for the electron actually going through the left slit since, in actuality, it didn't. God Bless :)

      Delete
    2. theunnoticableFebruary 13, 2022 at 5:15 PM

      I guess I don't see how there isn't a truth-maker for the electron actually going through the left slit. It seems to me that if chance favored the left slit, then that would be a truth-maker.

      Delete

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