I now return to the question I posed earlier. According to Smart, canonical laws of nature are of the form “All Fs are Gs until t”. Now, we supposed earlier that until 2019 it has indeed been true that in the universe all F’s have been Gs, but that it will happen that next year a non-G F will occur. On Smart’s view, then, in 2019 it will be a law that “All Fs are G until 2019” but that in 2020 it will not be a law that “All Fs are G until 2020”. My question was: have, therefore, the laws of nature changed, or not? Now, Hume himself never explicitly considered whether the laws of nature can change, but his implicit position was they cannot. This is because his implicit view, as mentioned, is that the laws of nature are those regularities that have held up until this point and that will continue to hold in the future (whether we know they will or not). And so, on Hume’s view, if “All Fs are Gs” were true up until 2019, although we might think that this is a law of nature (again, due to custom or habit), when in 2020 a nonG F occured, we would then have to admit that it not only isn’t a law of nature in 2020, but that it never was a law of nature at all. But Smart himself cannot allow this. This is because on his view, it seems, when 2019 is present he must say it is a law of nature that “All Fs are G until 2019”. And in fact, the fact that when 2020 comes along and a non G F occurs, does not stop this from being a law of nature, for it is still true in 2020 that “All Fs are Gs until 2019”. And so, it seems, Smart must admit that laws of nature are all of them relative to times. That is, there is one set of laws that are true relative to 2019, and another set relative to 2020, and so on.
Indeed, if “All Fs are Gs until 2019” is a law, when it was 2018 it would have ben true that “All Fs are Gs until 2018” was a law. But, this law, as it contains the
qualifier 2019. As such, Smart is committed to there being a different set of laws for
every moment of time. Each of these sets of laws comes into existence as the time it
refers to does (“All Fs are Gs until 1999” came into existence in 1999 when this year came into existence, “All Fs are Gs until 2000” came into existence in 2000 when this year came into existence, and so on). But each of these laws will continue to hold no matter what happens in the future too, for nothing that can happen after a certain time t can have any influence over what happened until t.
All of the above is quite difficult to square with Hume’s view itself. After all, Hume did not think that there were laws that are relative to times, or that laws could continue to hold even if the regularities they mention cease to hold (for, on his view, then they wouldn’t have been a law at all). So, Smart’s view turns out not to be as “true-to-Hume” as he thinks it is. In what follows I develop an account that I believe is truer-to-Hume’s.
My basic idea is that, if the growing block view is true, then because the future has not yet happened, we should not admit that there are any laws at all. Now, Hume himself never considered the open future, or the idea of there being a growing block. But it seems likely that if were to accept that there are no facts about the future, i.e. that it is alethiclly open, then he would have admitted that there is no truth about whether any regularity will continue to hold or not either. And as a consequence, he would have held no regularity that has occured up until now can possibly be a law.
Of course, the above does not prevent us from defining a weaker notion, something that we might call a ‘potential-law’. A potential-law, as we might think of it, is a regularity that has held up until the current moment, and so can supervene on the four dimensional mosaic that currently exists (i.e. up to the edge of the growing block). It might then be that “All Fs are Gs” is indeeed a potential-law, even if it is not
law. We do not want to build any temporal qualifiers into these potential-laws because we will want to say that the if a regularity has held up until the current moment, then the very same potential law has held up until now. However, what we will want to say is that, if the regularity breaks down, and a non G F occurs (again, say, in 2020), then the potential-law will break down at that point to. Thus, we will say:
A statement of the form “All Fs are Gs” is a potential law at t iff all Fs have been G up until t.
That is, we build the temporal qualifier not into the statement of the potential-law itself, but into the conditions of its holding. This will then enable us to say that “All Fs are Gs” was a potential-law from the beginning of time up until 2020, when it stopped being a potential-law.
That, then, is my proposal. I believe this account, in terms of potential-laws, is a genuine “true-to-Hume” account of the laws of nature, for if Hume had accepted the open future, he would have denied that the regularities that have held up until this point count as being laws at all. But, it still enables us to recognise the importance of regularities in our causal thinking. There are single potential laws that hold until the regularities they embody break down (if they do break down). The potential-laws supervene on the currently existing extent of the growing block, and do not require there to be a more extensive subvenient base.
Moreover, as above mentioned, Lewis (1973: 75) defines the theory of counterfactuals by saying that it is a matter of comparative similarities. More
the first world shares more similarities with the actual one than the second. That being said, by adopting the concept of potential laws to the discussion of temporality, it enables one to also explain how we measure closeness of possible worlds the way Lewis would intend, and so it is consistent with his account of causation in terms of counterfactual conditionals. And finally, if the end of time ever comes, and a regularity has held throughout all of time, then a potential law will finally become a genuine law, in agreement with how Hume thought of them.
That completes my discussion of my positive view of how to combine the growing block view with Humeanism. Before finishing, in what follows I discuss some further issues in light of this proposal in a more speculative manner.