quote:
The reason that tentativity is important in science is because it is an acknowledgement of the fact that we can never knowingly have ALL of the relevant evidence. It is an acknowledgement of the very practical limitations imposed on knowledge and certainty. It is an acknowledgement of the possibility that new evidence can turn up that will completely blow away much of what we think we know.
As applied to the number of legs you have (or other such examples) the whole things is fairly academic as the only way such conclusions could be wrong is if you are a "brain in a jar", dweller in a matrix or some other equally pointlessly irrefutable philosophical consideration.
However tentativity as an acknowledgement of the very practical fact that we can never knowingly have all of the relevant evidence is a rather key aspect of any discourse that seeks to consider how confident we can be in our evidence or the conclusions that we derive from our evidence. This remains true no matter how many legs you may or may not have.
As I've said earlier in this thread, in actual scientific practice we would normally consider the fact that Dr Adequate has two legs to be an "observation" or "data." We would normally not speak of his two legs as a "theory" or as "proven" (or "regarded as proven"). The observation that he has two legs is tentative, but only slightly so. If it turns out we were wrong, we would normally explain this as bad data or an incorrect observation.
As you say, tentativity is important in science because we can never have all of the evidence. And we don't know which evidence we may have misinterpreted. In order to figure out the unknown, we must juggle data with varying degrees of probability as to their correctness. We are comfortable with some measure of uncertainty. This is in contrast to engineering, where uncertainty is generally not acceptable.