Will the sun rise tomorrow?

The sun has always risen in the past, but does that mean it will definitely rise tomorrow morning?


The book which Phoebe has been reading is An Enquiry Concerning Human Understanding by David Hume, an 18th Century Scottish philosopher.

Hume was an empiricist. He believed that all knowledge must be based on the evidence of the senses. But, he points out, we only have evidence from the senses about the workings of the world in the present and the past. Obviously we have no evidence about the future because it hasn't happened yet. So we cannot be sure what the future will bring. We cannot even be sure that the sun will rise tomorrow.

Most people get round this problem in the way that Philip suggests: for the last several thousand years the sun has risen as usual. So it will do so tomorrow as well. But this is a circular argument: it involves the belief that the future must behave in the same way as the past. So because the sun always has risen it always will.

What evidence is there for this belief? There is lots of evidence for it being true in the past. We know that nature behaved the
same way in 2001 CE as in 2000 CE for example, because we were there watching it. And the same is true for 2002 CE
compared with 2001 CE. So, in the past, the future always has turned out to be the same as the earlier past.

But will this continue? Can we be sure it will behave the same way in 2020CE as it currently does? No, we cannot be sure, says
Hume. We will just have to wait and see.

* * *

Once you have understood Hume's argument there is very little chance of proving it wrong. Phoebe has seen this, and that is why
she is so worried! She is correct; it is impossible to prove that the sun will rise tomorrow.

But perhaps she is overreacting by being so worried. There are lots of other things that are more likely to give us trouble than
the failure of the sun to rise (global warming, financial crises, diseases, terrorism, old age ...), so perhaps she is worried about
the wrong thing. And anyway, isn't it be better to be excited about the future being different, rather than worried?

So, although Phoebe is philosophically more correct, Philip is more sensible in his approach to life in an uncertain world. As Hume
says at the end of his book: there comes a point where you just have to leave such philosophical musings to one side and get on
with life!

Extra tricky questions for budding philosophers

  1. Science is based on experiments using sense experience, so can it predict the future?
  2. Why do scientific laws stay the same year after year? Why don't they change like everything else?
  3. Which matters more: security or adventure?

You can read the relevant section of Hume's book for yourself by clicking here.