First of all,
Good question.
Second of all,
They are right, there is no document which states what is to be accepted as evidence and what is to be rejected.
To help answer this question a little more in depth, I would like to propose the following.
I believe that science exhitbits nine characterisitcs. And no this is not entirely my own list, I have colloborated with a great professor [my opnion] in my own list of characterisitcs and have modified mine when it needed to be modified. I will only list the relative ones that will relate to this question.
1. SCIENCE IS BASED ON EVIDENCE - well duh, but what kind? Physical, Observable and Empirical. Evidence does not always have to come from controlled experiments. Obviously the Thoery of Relativity did not come from experimentation when it was first formulated.
2. IT IS TESTABLE - Based on the evidence we can formulate a hypothesis, but is must be testable. You can state how you would theoretically test it, again the thoery of relativity, which was not proven until a few years ago.
4. IT IS PUBLIC - All observations and results of testing is made public to the rest of the scientific communinity for verification and acceptance. It is not kept private - for that would not be science in its strictest sense.
5. IT IS SELF-CORRECTING - which merely states that science does make mistakes - take a look at the early models of cell membranes or the atom. Why is it self-correcting? Becuase it is made public, therefore others can test the findings and if they duplicate it - fine, if not, then it needs to either be revised or rejected.
6. IT IS NON-AUTHORITARIAN - There is no one expert who is the President of science who dictates how things have to be done or what evidence is accepted or rejected. That is why there is no document or source that lays down the law. Science is all about learning the world around us, how would we learn about it in a fair and unbiased way if there was a standard in how we could do it - ex. someone dictating evidence acceptance criteria. Now granted we have standard procedures for certain things, ex. physical constants, laws, things of that nature.
7. IT IS CONSENSUAL - Example - We accept that the model that best works for us in regards to the cell membrane is the fluid-mosiac model. Why? Becuase it is accepted by most of the scientific community of biology. There is a consensus that this model is correct as of today - not to say it may change with new evidence someday.
8. IT IS TENTATIVE - Science changes as new things are discovered. Again one of the models of the cell membrane was the sandwich model. Did not work, when the electron microscope came on the scene around the 1950s. The model was changed based upon the new evidence.
All nine do relate to this question. Based on the above characterisitcs of science [or I should say good science], evidence to be accepted must meet all these requirements. It does need to be based off something we can see or gather data in whether it is application in nature or theoretical in nature. It needs to be public so it can see if it can gain acceptance by the consensus of the scientific community. If it can, then this would be good evidence to accept. If it cannot fit the criterium then you would really need to think hard about accepting it. If it does not fit this criterium, it does not belong to the Magesterium of Science, it would belong to another Magesteria.
Hope this helped.
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