As a follow on from this question.
How do you counter to argument, which I will nickname “Argumentum ab ignavia” which goes along the pseudo Socratic lines of:
“I have no real evidence on your proposition 'that the sun will rise tomorrow', (even though I could access evidence from the internet in a matter of minutes I would rather not) and therefore the sun’s status tomorrow morning is therefore unknowable”
The proposition the sun will rise tomorrow is one for which proof can be added within the scientific paradigm.
However, as un-intelligent as it may seem in certain contexts, (what is usually labelled as) philosophical doubt is broader than the forming of scientifically theory. The scientific doubt is not yet a scientifically proven statement, since rigorous validation of hypotheses should be added; even though good scientists are of course aware of the always lurking uncertainty, and would of course incorporate any evidence for the contrary. Even a scientist can think of many ways in which the sun could be destroyed or blocked from our view, etc...; however, for the moment there is no evidence to confirm such an hypothesis.
A way to counter this argument could be to ask the stater of the proposition you mentioned in your question (I can not know): What exactly do you mean by knowledge then?
Since the person asking the question could be conceived as a lunatic: his definition of knowledge might be so strict, or perhaps so non-existing, or non-findable; that his own model of knowledge can certainly be put into question (see many examples in the history of philosophy: perhaps to start with Parmenides). These ideals of knowledge say something about our wish for stability, and can function as an ideal; but they can be interpreted in very un-sensible ways.
It is also very conceivable that such a man is indeed very ignorant, so then this would be an accurate proposition. There are many diseases which make man unable to think properly or hallucinate. Some human beings are born without indeed ever understanding the temporal repetitive orbits of the earth relative to the sun.
Further more, at some point in time, many children or adults discovering philosophical fundamental questions might discover the possibility to ask themselves these questions, or to doubt about normally firmly likely propositions. I hope myself that people can nevertheless eventually conquer this doubt in a healthy and vigorous way.
These questions can even make man so uncomfortable with their world-view, certainly when this doubt remains very prominently for a very long time, that this might in some cases be coupled with severe mental problems, which should be taken seriously; in those cases.
But then again: this highly depends on the personal interpretation, context and magnitude of the doubt. Doubt can also be conceived of as an healthy asset, when it is not overwhelming, at least not about such propositions for which there is no evidence available. The best thing they can lead to, is to doubt about more dubious propositions. Generally, the doubt often can incite (or show) an important wish to actively prove, since they are coupled with the amazing aspect of human life: the mysterious.
